Revert "arm64: Kconfig: Make SME depend on BROKEN for now"

This reverts commit 81235ae0.

With SME forcefully disabled at runtime, we can flip CONFIG_ARM64_SME
back on so that the associated KMI changes can be merged ahead of the
freeze.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Todd Kjos <tkjos@google.com>
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 393087661
Change-Id: If9567f6693bd4e4def966e51d329bbd47daf7c3f