Add a decoding union for the bits in control registers 2 and use
'union ctlreg0' and 'union ctlreg2' in update_cr_regs to improve
readability.
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>