UPSTREAM: arm64: tlbflush: avoid flushing when fullmm == 1

The TLB gather code sets fullmm=1 when tearing down the entire address
space for an mm_struct on exit or execve. Given that the ASID allocator
will never re-allocate a dirty ASID, this flushing is not needed and can
simply be avoided in the flushing code.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Bug: 31432001
Change-Id: I59e4d71b33bf7760466becfa4ea3513d0ad9bdae
(cherry picked from commit 5a7862e83000ccfd36db927c6f060458fe271157)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>