[DEVMEM] uses DEV_MEM instead of hardcoded /dev/mem

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[DAVINCI] Fix FlipRegion and UpdateRegion

This fixes the compilation but I have not tested it as I don't have
a Davinci board.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>