arm: Disable the VFP during boot

The VFP code expects the kernel to boot with VFP disabled, but some
boards will boot with it enabled. Make sure that vfp_init() disables
the VFP on each CPU during boot.

PR: 273752
Reviewed by: andrew
Diagnosed by: Thomas Skibo <thomas-bsd@skibo.net>
MFC after: 1 week