target/arm: Restrict the values of DCZID.BS under TCG

target/arm: Restrict the values of DCZID.BS under TCG

We can simplify our DC_ZVA if we recognize that the largest BS
that we actually use in system mode is 64.  Let us just assert
that it fits within TARGET_PAGE_SIZE.

For DC_GVA and STZGM, we want to be able to write whole bytes
of tag memory, so assert that BS is >= 2 * TAG_GRANULE, or 32.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200626033144.790098-18-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>