arm64: update linker script to increased L1_CACHE_BYTES value

Bring the linker script in line with the recent increase of
L1_CACHE_BYTES to 128. Replace the hardcoded value of 64 with the
symbolic constant.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
[catalin.marinas@arm.com: fix up RW_DATA_SECTION as well]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>