VFPv4 support depends on the VFPv3 context save/restore code, so only
advertise support in the hwcaps if the kernel can actually handle it.

Cc: <stable@vger.kernel.org> # 3.1+
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>