arm64/sme: Include ID_AA64PFR1_EL1.SME in cpu-feature-registers.rst

We expose ID_AA64PFR1_EL1.SME to userspace but do not document this in
cpu-feature-registers.rst. Add it.
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230914-arm64-pfr1-sme-doc-v1-1-b6c497d10d77@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

Documentation/arch/arm64/cpu-feature-registers.rst

@@ -175,6 +175,8 @@ infrastructure:
      +------------------------------+---------+---------+
      | Name                         |  bits   | visible |
      +------------------------------+---------+---------+
+     | SME                          | [27-24] |    y    |
+     +------------------------------+---------+---------+
      | MTE                          | [11-8]  |    y    |
      +------------------------------+---------+---------+
      | SSBS                         | [7-4]   |    y    |