arm64: Report address tag when FEAT_MTE_TAGGED_FAR is supported

arm64: Report address tag when FEAT_MTE_TAGGED_FAR is supported

If FEAT_MTE_TAGGED_FAR (Armv8.9) is supported, bits 63:60 of the fault address
are preserved in response to synchronous tag check faults (SEGV_MTESERR).

This patch modifies below to support this feature:
  - Use the original FAR_EL1 value when an MTE tag check fault occurs,
    if ARM64_MTE_FAR is supported so that not only logical tag
    (bits 59:56) but also address tag (bits 63:60] being reported too.

  - Add HWCAP for mtefar to let user know bits 63:60 includes
    address tag information when when FEAT_MTE_TAGGED_FAR is supported.

Applications that require this information should install
a signal handler with the SA_EXPOSE_TAGBITS flag.
While this introduces a minor ABI change,
most applications do not set this flag and therefore will not be affected.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Link: https://lore.kernel.org/r/20250618084513.1761345-3-yeoreum.yun@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>