ARM: VFP: add support to sync the VFP state of the current thread

BugLink: http://bugs.launchpad.net/bugs/507503

So far vfp_sync_state worked only for threads other than the current
one. This worked for tracing other threads, but not for PTRACE_TRACEME.
Syncing for the current thread will also be needed by an upcoming patch
adding support for VFP context save / restore around signal handlers.

For SMP we need get_cpu now, since we have to protect the FPEXC
register, other than this things remained the same for threads other
than the current.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>