target/ppc: Implement SPRC/SPRD SPRs

This implements the POWER SPRC/SPRD SPRs, and SCRATCH0-7 registers that
can be accessed via these indirect SPRs.

SCRATCH registers only provide storage, but they are used by firmware
for low level crash and progress data, so this implementation logs
writes to the registers to help with analysis.

Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
6 files changed