tcg/arm: Improve tlb load for armv7

Use UBFX to avoid limitation on CPU_TLB_BITS.  Since we're dropping
the initial shift, we need to replace the page masking.  We can use
MOVW+BIC to do this without shifting.  The result is the same size
as the armv6 path with one less conditional instruction.

Signed-off-by: Richard Henderson <rth@twiddle.net>
