refactor(aarch64): remove `FEAT_BTI` architecture check

BTI instructions are a part of the NOP space in earlier architecture
versions, so it's not inherently incorrect to enable BTI code
or instructions even if the target architecture does not support them.

This change reduces our reliance on architecture versions when checking
for features.

Change-Id: I79f884eec3d65978c61e72e4268021040fd6c96e
Signed-off-by: Chris Kay <chris.kay@arm.com>
1 file changed