board: laird: wb50n: use configure_ddrcfg_input_buffers

Replace code with new function configure_ddrcfg_input_buffers from SFR
mach driver.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
diff --git a/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index ad09731..ce0b1b4 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -292,6 +292,7 @@
 	select BOARD_LATE_INIT
 	select CPU_V7A
 	select SUPPORT_SPL
+	select ATMEL_SFR
 
 endchoice