FROMLIST: arm64: mm: Add arm64_kernel_unmapped_at_el0 helper

In order for code such as TLB invalidation to operate efficiently when
the decision to map the kernel at EL0 is determined at runtime, this
patch introduces a helper function, arm64_kernel_unmapped_at_el0, to
determine whether or not the kernel is mapped whilst running in userspace.

Currently, this just reports the value of CONFIG_UNMAP_KERNEL_AT_EL0,
but will later be hooked up to a fake CPU capability using a static key.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git


 commit fc0e1299da548b32440051f58f08e0c1eb7edd0b)
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Change-Id: I5f8c15e5f8ba0c521d0ed7515c003598bf3d7cf8
Git-Commit: 1434f49f
Git-repo: git://android.googlesource.com/kernel/common.git


[vinmenon@codeaurora.org: trivial merge conflicts]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>