x86: fix fpu restore from sig return

If the task never used fpu, initialize the fpu before restoring the FP
state from the signal handler context. This will allocate the fpu
state, if the task never needed it before.

Reported-and-bisected-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Tested-by: Eric Sesterhenn <snakebyte@gmx.de>
Cc: Frederik Deweerdt <deweerdt@free.fr>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>