target/ppc: Rename sfprf to sfifprf where it's also used as set fi flag

The bit FI fix used the sfprf flag as a flag for the set_fi parameter
in do_float_check_status where applicable. Now, this patch rename this
flag to sfifprf to state this dual usage.

Signed-off-by: Víctor Colombo <[email protected]>

Author: vcoracolombo