exec: Add both big- and little-endian memory helpers

Step three in the transition: helpers not tied to the target
"default" endianness.  To be used when the guest uses a memory
operation with non-default endianness.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-i386: Tidy softmmu routines

Pass two TCGReg to tcg_out_tlb_load, rather than idx+args.

Move ldst_optimization routines just below tcg_out_tlb_load to avoid
the need for forward declarations.

Use TCGReg enum in preference to int where apprpriate.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-i386: Remove "cb" output restriction from qemu_st8 for i386

Once we form a combined qemu_st_i32 opcode, we won't be able to
have separate constraints based on size.  This one is fairly easy
to work around, since eax is available as a scratch register.

When storing variable data, this tends to merely exchange one mov
for another.  E.g.

-:  mov    %esi,%ecx
...
-:  mov    %cl,(%edx)
+:  mov    %esi,%eax
+:  mov    %al,(%edx)

Where we do have a regression is when storing constant data, in which
we may load the constant into edi, when only ecx/ebx ought to be used.

The proper way to recover this regression is to allow constants as
arguments to qemu_st_i32, so that we never load the constant data into
a register at all, must less the wrong register.  TBD.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-i386: Support new ldst opcodes

No support for helpers with non-default endianness yet,
but good enough to test the opcodes.

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-ppc: Convert to new ldst opcodes

This lets us change "le_mode" to "end_mode" and fold away nearly all
of the tests for the current cpu endianness, and removing all of the
explicitly generated bswap opcodes.

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