arm64: Add cpus_have_final_boot_cap()

The cpus_have_final_cap() function can be used to test a cpucap while
also verifying that we do not consume the cpucap until system
capabilities have been finalized. It would be helpful if we could do
likewise for boot cpucaps.

This patch adds a new cpus_have_final_boot_cap() helper which can be
used to test a cpucap while also verifying that boot capabilities have
been finalized. Users will be added in subsequent patches.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>