target-ppc: Switch POWER7/8 classes to use correct PMU SPRs

target-ppc: Switch POWER7/8 classes to use correct PMU SPRs

This replaces gen_spr_7xx() call (which registers 32bit SPRs) with
gen_spr_book3s_pmu() call.

This removes SPR_7XX_PMC5/6 as they are for 32bit and gen_spr_book3s_pmu()
already registers correct PMC5/6 SPRs.

This removes explicit MMCRA registration as gen_spr_book3s_pmu() does it
anyway.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>