accel/tcg: Unify cpu_{ld,st}*_{be,le}_mmu

accel/tcg: Unify cpu_{ld,st}*_{be,le}_mmu

With the current structure of cputlb.c, there is no difference
between the little-endian and big-endian entry points, aside
from the assert.  Unify the pairs of functions.

The only use of the functions with explicit endianness was in
target/sparc64, and that was only to satisfy the assert: the
correct endianness is already built into memop.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>