target-ppc: Consolidate instruction decode helpers

target-ppc: Consolidate instruction decode helpers

Move instruction decode helpers to target-ppc/internal.h so that some
of these can be used from outside of translate.c. This movement also
helps to get rid of some duplicate helpers from target-ppc/fpu_helper.c.

Suggested-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>