tcg: Add page_bits and page_mask to TCGContext

Disconnect guest page size from TCG compilation.
While this could be done via exec/target_page.h, we want to cache
the value across multiple memory access operations, so we might
as well initialize this early.

The changes within tcg/ are entirely mechanical:

    sed -i s/TARGET_PAGE_BITS/s->page_bits/g
    sed -i s/TARGET_PAGE_MASK/s->page_mask/g

Reviewed-by: Anton Johansson <anjo@rev.ng>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>