[media] OMAP_VOUT: CLEANUP: Make rotation related helper functions more descriptive

Rename rotation_enabled() and rotate_90_or_270() to is_rotation_enabled()
and is_rotation_90_or_270() to make them more descriptive.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>