x86/its: explicitly manage permissions for ITS pages

execmem_alloc() sets permissions differently depending on the kernel
configuration, CPU support for PSE and whether a page is allocated
before or after mark_rodata_ro().

Add tracking for pages allocated for ITS when patching the core kernel
and make sure the permissions for ITS pages are explicitly managed for
both kernel and module allocations.

Fixes: 872df34d ("x86/its: Use dynamic thunks for indirect branches")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20250603111446.2609381-5-rppt@kernel.org