nouveau: Fix endianness with new context program loader

When switching to request_firmware() to load the context programs,
some endian fixes need to be applied. This makes it work again on
my quad g5 nvidia 6600.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>