[ARM] arm32ve: Implement context switching for VFPv3

This patch adds support for switching VFPv3 context in arm32ve
port. This VFPv3 context switching will only work if underlying
host hardware has support for VFPv3 or higher. If underlying
hardware has VFPv2 or lower then all floating point accesses
from VCPU will be trapped and VCPU will be halted.

In future, it is highly unlikely that CPU vendors will come-up
with a ARMv7 CPU with virtualization extension but VFPv2 or lower.

Signed-off-by: Anup Patel <anup@brainfault.org>