arm/arm64: assembler.h: Replace size with end address for dcache_by_line_op

Commit b5f659be ("arm/arm64: Remove dcache_line_size global
variable") moved the dcache_by_line_op macro to assembler.h and changed
it to take the size of the regions instead of the end address as
parameter. This was done to keep the file in sync with the upstream
Linux kernel implementation at the time.

But in both places where the macro is used, the code has the start and
end address of the region, and it has to compute the size to pass it to
dcache_by_line_op. Then the macro itsef computes the end by adding size
to start.

Get rid of this massaging of parameters and change the macro to the end
address as parameter directly.

Besides slightly simplyfing the code by remove two unneeded arithmetic
operations, this makes the macro compatible with the current upstream
version of Linux (which was similarly changed to take the end address in
commit 163d3f80695e ("arm64: dcache_by_line_op to take end parameter
instead of size")), which will allow us to reuse (part of) the Linux C
wrappers over the assembly macro.

The change has been tested with the same snippet of code used to test
commit 410b3bf0 ("arm/arm64: Perform dcache clean + invalidate after
turning MMU off").

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>