spl: move SYS_OS_BASE to Kconfig

Move SYS_OS_BASE to Kconfig and cleanup existing
uses.

Signed-off-by: Heiko Schocher <hs@denx.de>
[trini: Also migrate a4m2k]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/a4m2k_defconfig b/configs/a4m2k_defconfig
index c54689d..144291e 100644
--- a/configs/a4m2k_defconfig
+++ b/configs/a4m2k_defconfig
@@ -12,6 +12,7 @@
 CONFIG_SPL=y
 CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_SPL_OS_BOOT=y
+CONFIG_SYS_OS_BASE=0xfc200000
 CONFIG_HUSH_PARSER=y
 CONFIG_LOOPW=y
 # CONFIG_CMD_SETEXPR is not set