KVM: arm64: Minor optimization of range_is_memory

Currently range_is_memory finds the corresponding struct memblock_region
for both the lower and upper bounds of the given address range with two
rounds of binary search, and then checks that the two memblocks are the
same. Simplify this by only doing binary search on the lower bound and
then checking that the upper bound is in the same memblock.

Signed-off-by: David Brazdil <dbrazdil@google.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210728153232.1018911-3-dbrazdil@google.com