target-ppc: add support for extended mtfsf/mtfsfi forms

Power ISA 2.05 adds support for extended mtfsf/mtfsfi form, with a new
W field to select the upper part of the FPCSR register.

For that the helper is changed to handle 64-bit input values and mask with
up to 16 bits. The mtfsf/mtfsfi instructions do not have the W bit
marked as invalid anymore. Instead this is checked in the helper, which
therefore needs to access to the insns/insns_flags2. They are added in
the DisasContext struct. Finally change all accesses to the opcode fields
through extract helpers, prefixed with FP for consistency.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Alexander Graf <agraf@suse.de>
