PowerPC: Fix encoding of rldimi and rldcl instructions

When testing the asm parser, I noticed wrong encodings for the
above instructions (wrong operand name in rldimi, wrong form
and sub-opcode for rldcl).

Tests will be added together with the asm parser.
PowerPC: Fix encoding of stfsu and stfdu instructions

When testing the asm parser, I noticed wrong encodings for the
above instructions (wrong sub-opcodes).  Note that apparently
the compiler currently never generates pre-inc instructions
for floating point types for some reason ...

Tests will be added together with the asm parser.
PowerPC: Fix encoding of vsubcuw and vsum4sbs instructions

When testing the asm parser, I noticed wrong encodings for the
above instructions (wrong sub-opcodes).

Tests will be added together with the asm parser.