arm64: mte: Define the number of bytes for storing the tags in a page

arm64: mte: Define the number of bytes for storing the tags in a page

Rather than explicitly calculating the number of bytes for a compact tag
storage format corresponding to a page, just add a MTE_PAGE_TAG_STORAGE
macro. With the current MTE implementation of 4 bits per tag, we store
2 tags in a byte.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Luis Machado <luis.machado@linaro.org>
Link: https://lore.kernel.org/r/20220131165456.2160675-4-catalin.marinas@arm.com
Signed-off-by: Will Deacon <will@kernel.org>