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/microblaze-generic_defconfig b/configs/microblaze-generic_defconfig
index bc97f60..3dbf48a 100644
--- a/configs/microblaze-generic_defconfig
+++ b/configs/microblaze-generic_defconfig
@@ -16,6 +16,7 @@
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_SPL_OS_BOOT=y
+CONFIG_SYS_OS_BASE=0x2c060000
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot-mONStR> "
 CONFIG_CMD_ASKENV=y