ARM: 7399/1: vfp: move user vfp state save/restore code out of signal.c

ARM: 7399/1: vfp: move user vfp state save/restore code out of signal.c

The user VFP state must be preserved (subject to ucontext modifications)
across invocation of a signal handler and this is currently handled by
vfp_{preserve,restore}_context in signal.c

Since this code requires intimate low-level knowledge of the VFP state,
this patch moves it into vfpmodule.c.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>