KVM: arm64: Stop writing aarch32's CSSELR into ACTLR

aarch32 has pairs of registers to access the high and low parts of 64bit
registers. KVM has a union of 64bit sys_regs[] and 32bit copro[]. The
32bit accessors read the high or low part of the 64bit sys_reg[] value
through the union.

Both sys_reg_descs[] and cp15_regs[] list access_csselr() as the accessor
for CSSELR{,_EL1}. access_csselr() is only aware of the 64bit sys_regs[],
and expects r->reg to be 'CSSELR_EL1' in the enum, index 2 of the 64bit
array.

cp15_regs[] uses the 32bit copro[] alias of sys_regs[]. Here CSSELR is
c0_CSSELR which is the same location in sys_reg[]. r->reg is 'c0_CSSELR',
index 4 in the 32bit array.

access_csselr() uses the 32bit r->reg value to access the 64bit array,
so reads and write the wrong value. sys_regs[4], is ACTLR_EL1, which
is subsequently save/restored when we enter the guest.

ACTLR_EL1 is supposed to be read-only for the guest. This register
only affects execution at EL1, and the host's value is restored before
we return to host EL1.

Rename access_csselr() to access_csselr_el1(), to indicate it expects
the 64bit register index, and pass it CSSELR_EL1 from cp15_regs[].

Signed-off-by: James Morse <james.morse@arm.com>
----
Providing access_csselr_cp15() wouldn't work as with VHE CSSELR_EL1 is
loaded on the CPU while this code runs. access_csselr_cp15() would have
to map it back the 64bit resgister to use vcpu_write_sys_reg(). We may
as well do it in the table.

Because of this, I suspect aarch32 fault injection is broken for aarch32
guests of a VHE host.... (a bug for next week).