PowerPC64 little-endian fixes: 32-bit DFP parameters

PowerPC64 little-endian fixes: 32-bit DFP parameters

Passing a 32-bit DFP in register needs to use the least-significant part
of the register.  Like with a previous patch that addressed the same
issue for small structs, this patch makes sure the appropriate offset
is used on little-endian systems.

gdb/ChangeLog:

	* ppc-sysv-tdep.c (ppc64_sysv_abi_push_freg): Use correct
	offset on little-endian when passing _Decimal32.
	(ppc64_sysv_abi_return_value_base): Likewise for return values.