This corrects the save/restore code in mca_asm.S
which was written long ago, before the assembler understood
mnemonic names for 'cr' and 'ar' registers (in fact it
appears to have been written pre-silicon, some of the
control register numbers don't match with what actually
got built).  There were other goofs too (like using
0, 1, 2, etc. for region register subscripts).