UPSTREAM: arm64: mm: use bit ops rather than arithmetic in pa/va translations

UPSTREAM: arm64: mm: use bit ops rather than arithmetic in pa/va translations

Since PAGE_OFFSET is chosen such that it cuts the kernel VA space right
in half, and since the size of the kernel VA space itself is always a
power of 2, we can treat PAGE_OFFSET as a bitmask and replace the
additions/subtractions with 'or' and 'and-not' operations.

For the comparison against PAGE_OFFSET, a mov/cmp/branch sequence ends
up getting replaced with a single tbz instruction. For the additions and
subtractions, we save a mov instruction since the mask is folded into the
instruction's immediate field.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Bug: 30369029
Patchset: kaslr-arm64-4.4

(cherry picked from commit 8439e62a15614e8fcd43835d57b7245cd9870dc5)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I1ea4ef654dd7b7693f8713dab28ca0739b8a2c62