target-ppc: fix bit extraction for FPBF and FPL

target-ppc: fix bit extraction for FPBF and FPL

Bit extraction for the FP BF and L field of the MTFSFI and MTFSF
instructions is wrong and doesn't match the reference manual (which
explain the bit number in big endian format). It has been broken in
commit 7d08d85645def18eac2a9d672c1868a35e0bcf79.

This patch fixes this, which in turn fixes the problem reported by
Khem Raj about the floor() function of libm.

Reported-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
CC: qemu-stable@nongnu.org (1.6)
Signed-off-by: Alexander Graf <agraf@suse.de>