arm/arm64: Remove dcache_line_size global variable

Compute the dcache line size when doing dcache maintenance instead of using
a global variable computed in setup(), which allows us to do dcache
maintenance at any point in the boot process. This will be useful for
running as an EFI app and it also aligns our implementation to that of the
Linux kernel. As a result, the dcache_by_line_op assembly has been modified
to take a range described by start address and size, instead of start and
end addresses.

For consistency, the arm code has been similary modified.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>