target-ppc: Add POWER8's FSCR SPR

This adds an FSCR (Facility Status and Control Register) SPR. This defines
names for FSCR bits.

This defines new exception type - POWERPC_EXCP_FU - "facility unavailable" (FU).
This registers an interrupt vector for it at 0xF60 as PowerISA defines.

This adds a TCG helper_fscr_facility_check() helper to raise an exception
if the facility is not enabled. It updates the interrupt cause field
in FSCR. This adds a TCG translation block generation code. The helper
may be used for HFSCR too as it has the same format.

The helper raising FU exceptions is not used by this patch but will be
in the next ones.

This adds gen_update_current_nip() to update NIP in DisasContext.
This helper is not used now and will be called before checking for
a condition for throwing an FU exception.

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