ARM: 7756/1: zImage/virt: remove hyp-stub.S during distclean

Make sure hyp-stub.S gets removed during make distclean,
this left over file was introduced in commit:

424e5994

 ARM: zImage/virt: hyp mode entry support for the zImage loader

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Dave Martin <dave.martin@linaro.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>