kselftest/arm64: Add FPMR coverage to fp-ptrace

Add coverage for FPMR to fp-ptrace. FPMR can be available independently of
SVE and SME, if SME is supported then FPMR is cleared by entering and
exiting streaming mode. As with other registers we generate random values
to load into the register, we restrict these to bitfields which are always
defined. We also leave bitfields where the valid values are affected by
the set of supported FP8 formats zero to reduce complexity, it is unlikely
that specific bitfields will be affected by ptrace issues.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241112-arm64-fp-ptrace-fpmr-v2-3-250b57c61254@kernel.org


[catalin.marinas@arm.com: use REG_FPMR instead of FPMR]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>