KVM: arm64: Remove internal accessor helpers for id regs

The internal accessors are only ever called once. Dump out their
contents in the caller.

No functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220913094441.3957645-3-oliver.upton@linux.dev