omap4: Definitions for SYS_BOOT-based fallback boot device selection

This introduces code to read the value of the SYS_BOOT pins on the OMAP4, as
well as the memory-preferred scheme for the interpretation of each value.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
diff --git a/arch/arm/cpu/armv7/omap4/Makefile b/arch/arm/cpu/armv7/omap4/Makefile
index 76a032a..564f1f6 100644
--- a/arch/arm/cpu/armv7/omap4/Makefile
+++ b/arch/arm/cpu/armv7/omap4/Makefile
@@ -5,6 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+obj-y	+= boot.o
 obj-y	+= sdram_elpida.o
 obj-y	+= hwinit.o
 obj-y	+= emif.o