drivers/video/Kconfig: specify the SoCs that make use of FB_IMX

FB_IMX is the framebuffer driver used by MX1, MX21, MX25 and MX27 processors.

Pass this information to the Kconfig text to make it clear.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>