omapfb: Fix linker error in drivers/video/omap/lcd_2430sdp.c

There is a linker error from lcd_2430sdp.c if CONFIG_TWL4030_CORE is not
set. This can be triggered on OMAP2 builds when OMAP3 or OMAP4 are not set.

drivers/built-in.o: In function `sdp2430_panel_disable':
drivers/video/omap/lcd_2430sdp.c:123: undefined reference to `twl_i2c_write_u8'
drivers/video/omap/lcd_2430sdp.c:124: undefined reference to `twl_i2c_write_u8'
drivers/built-in.o: In function `sdp2430_panel_enable':
drivers/video/omap/lcd_2430sdp.c:110: undefined reference to `twl_i2c_write_u8'
drivers/video/omap/lcd_2430sdp.c:112: undefined reference to `twl_i2c_write_u8'

Fix this by selecting the TWL4030_CORE for MACH_OMAP_2430SDP when building
with CONFIG_FB_OMAP as there is no own Kconfig entry for lcd_2430 and it is
compiled always when both MACH_OMAP_2430SDP and FB_OMAP are set.
Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap/Kconfig

@@ -5,6 +5,7 @@ config FB_OMAP
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
+	select TWL4030_CORE if MACH_OMAP_2430SDP
 	help
           Frame buffer driver for OMAP based boards.