ARM: 9424/1: vfp: Use vfp_state_hold() in vfp_sync_hwstate().

vfp_sync_hwstate() uses preempt_disable() followed by local_bh_disable()
to ensure that it won't get interrupted while checking the VFP state.
This harms PREEMPT_RT because softirq handling can get preempted and
local_bh_disable() synchronizes the related section with a sleeping lock
which does not work with disabled preemption.

Use the vfp_state_hold() to synchronize the access.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>