tcg/mips: fix broken CONFIG_TCG_PASS_AREG0 code

tcg/mips: fix broken CONFIG_TCG_PASS_AREG0 code

The CONFIG_TCG_PASS_AREG0 code for calling ld/st helpers was
broken in that it did not respect the ABI requirement that 64
bit values were passed in even-odd register pairs. The simplest
way to fix this is to implement some new utility functions
for marshalling function arguments into the correct registers
and stack, so that the code which sets up the address and
data arguments does not need to care whether there has been
a preceding env argument.

Based on commit 9716ef3b for ARM by Peter Maydell.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 18fec301cd2a38f72a5eeba2656a0c5b4fa69fb7)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>