ARM: uniphier: rework spl_boot_device() and related code

The current implementation has ugly switch statements here and there,
and duplicates similar code.  Rework it using table lookups for SoC
data and reduce code duplication.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/arch/arm/mach-uniphier/Makefile b/arch/arm/mach-uniphier/Makefile
index 7baec73..124a1c6 100644
--- a/arch/arm/mach-uniphier/Makefile
+++ b/arch/arm/mach-uniphier/Makefile
@@ -25,7 +25,7 @@
 endif
 
 obj-y += soc-info.o
-obj-y += boot-mode/
+obj-y += boot-device/
 obj-y += clk/
 obj-y += dram/