arm64: insn: Provide a better name for aarch64_insn_is_nop()

arm64: insn: Provide a better name for aarch64_insn_is_nop()

The current aarch64_insn_is_nop() has exactly one caller which uses it
solely to identify if the instruction is a HINT that can safely be stepped,
requiring us to list things that aren't NOPs and make things more confusing
than they need to be. Rename the function to reflect the actual usage and
make things more clear.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20200504131326.18290-3-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>