lcd: Implement lcd_printf()

lcd_printf() has a prototype in include/lcd.h but no implementation. Fix
this by borrowing the lcd_printf() implementation from the cogent board
code (which appears to use its own LCD framework.)

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Anatolij Gustschin <agust@denx.de>