i2c-pxa, rename BIT macro to PXA_BIT

BIT macro will be global definiton of (1 << x)
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Nicolas Pitre <nico@cam.org>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>