Kconfig: Convert CONFIG_SYS_SRAM_BASE to Kconfig

This converts ad-hoc CONFIG_SYS_SRAM_BASE to Kconfig.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
diff --git a/Kconfig b/Kconfig
index 54b3680..9f7707a 100644
--- a/Kconfig
+++ b/Kconfig
@@ -390,6 +390,11 @@
 	  SRAM base address is controlled by CONFIG_SYS_SRAM_BASE.
 	  SRAM size is controlled by CONFIG_SYS_SRAM_SIZE.
 
+config SYS_SRAM_BASE
+	hex
+	default 0x80000000 if TARGET_PIC32MZDASK
+	default 0x0
+
 endmenu		# General setup
 
 menu "Boot images"