firmware: arm_sdei: Make sdei_list_lock a raw spinlock

On an Ampere Altra,
Running a preemp_rt kernel based on v5.19-rc3-rt5 on an
Ampere Altra triggers:
[   15.683141] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
[   15.683154] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 24, name: cpuhp/0
[   15.683157] preempt_count: 0, expected: 0
[   15.683159] RCU nest depth: 0, expected: 0
[   15.683163] 3 locks held by cpuhp/0/24:
[   15.683167]  #0: ffffda30217c70d0 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
[   15.683201]  #1: ffffda30217c7120 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
[   15.683205]  #2: ffffda3021c711f0 (sdei_list_lock){....}-{3:3}, at: sdei_cpuhp_up+0x3c/0x130
[   15.683224] irq event stamp: 36
[   15.683226] hardirqs last  enabled at (35): [<ffffda301e85b7bc>] finish_task_switch+0xb4/0x2b0
[   15.683236] hardirqs last disabled at (36): [<ffffda301e812fec>] cpuhp_thread_fun+0x21c/0x248
[   15.683238] softirqs last  enabled at (0): [<ffffda301e80b184>] copy_process+0x63c/0x1ac0
[   15.683245] softirqs last disabled at (0): [<0000000000000000>] 0x0
[   15.683258] CPU: 0 PID: 24 Comm: cpuhp/0 Not tainted 5.19.0-rc3-rt5-[...]
[   15.683265] Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18
[   15.683268] Call trace:
[   15.683271]  dump_backtrace+0x114/0x120
[   15.683277]  show_stack+0x20/0x70
[   15.683279]  dump_stack_lvl+0x9c/0xd8
[   15.683288]  dump_stack+0x18/0x34
[   15.683289]  __might_resched+0x188/0x228
[   15.683292]  rt_spin_lock+0x70/0x120
[   15.683301]  sdei_cpuhp_up+0x3c/0x130
[   15.683303]  cpuhp_invoke_callback+0x250/0xf08
[   15.683305]  cpuhp_thread_fun+0x120/0x248
[   15.683308]  smpboot_thread_fn+0x280/0x320
[   15.683315]  kthread+0x130/0x140
[   15.683321]  ret_from_fork+0x10/0x20

sdei_cpuhp_up() is called in the STARTING hotplug section,
which runs whith interrupts disabled. Move CPUHP_AP_ARM_SDEI_
state to the _ONLINE section to execute the cpuhp cb with
preemption enabled.

Some SDEI calls (e.g. SDEI_1_0_FN_SDEI_PE_MASK) take actions on the
calling CPU. It is checked that preemption is disabled for them.
_ONLINE cpuhp cb are executed in the 'per CPU hotplug thread'.
Preemption is enabled in those threads, but their cpumask is limited
to 1 CPU.
Move 'WARN_ON_ONCE(preemptible())' statements so that SDEI cpuhp cb
don't trigger them. This means that no check will be done for some
cases, e.g. sdei_mask_local_cpu() invocations.

Also add a check for the SDEI_1_0_FN_SDEI_PRIVATE_RESET SDEI call
which acts on the calling CPU.

Suggested-by: James Morse <james.morse@arm.com>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>