docs/arm64: cpu-feature-registers: Documents missing visible fields

A couple of fields visible to userspace are not described in the
documentation. So update it.

Acked-by: Will Deacon <[email protected]>
Signed-off-by: Julien Grall <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>

Documentation/arm64/cpu-feature-registers.rst

@@ -193,6 +193,10 @@ infrastructure:
      +------------------------------+---------+---------+
      | Name                         |  bits   | visible |
      +------------------------------+---------+---------+
+     | SB                           | [36-39] |    y    |
+     +------------------------------+---------+---------+
+     | FRINTTS                      | [32-35] |    y    |
+     +------------------------------+---------+---------+
      | GPI                          | [31-28] |    y    |
      +------------------------------+---------+---------+
      | GPA                          | [27-24] |    y    |