arm64: idreg-override: Create a pseudo feature for rodata=off

Add rodata=off to the set of kernel command line options that is parsed
early using the CPU feature override detection code, so we can easily
refer to it when creating the kernel mapping.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-57-ardb+git@google.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>