backlight: ili9320: add missing SPI dependency

Add this missing SPI dependency and prevent the driver from building
without SPI, because functions of the spi driver are used in this
driver.

  drivers/video/backlight/ili9320.c:51: undefined reference to `spi_sync'

Also, a prompt string for CONFIG_LCD_ILI9320 is added for explicit
selection.
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/Kconfig

@@ -60,7 +60,8 @@ config LCD_LTV350QV
 	  The LTV350QV panel is present on all ATSTK1000 boards.
 
 config LCD_ILI9320
-	tristate
+	tristate "ILI Technology ILI9320 controller support"
+	depends on SPI
 	help
 	  If you have a panel based on the ILI9320 controller chip
 	  then say y to include a power driver for it.