V4L/DVB (7250): Clean up pxa-camera driver, remove non-functional and never tested pm-support

This patch addresses most issues pointed out by Russell and Erik, moves
recently introduced into pxa-regs.h camera-specific defines into
pxa_camera.c, removes dummy power-management functions, improves
function-naming, etc.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>