msm7630: Update for new memory map

New memory map for msm7630 with apps bootloader starting at
0x00100000 (1MB) and shared memory at 0x0.

Add new command "loadaddr:" to nandwrite for querying
the load address of images for flashing.  This allows the
target to respond with the second/larger memory segment
in order to accommodate larger images.
diff --git a/target/msm7630_surf/tools/mkheader.c b/target/msm7630_surf/tools/mkheader.c
index 9b03907..8701007 100644
--- a/target/msm7630_surf/tools/mkheader.c
+++ b/target/msm7630_surf/tools/mkheader.c
@@ -43,7 +43,11 @@
 	}
 
 	size = s.st_size;
+#if MEMBASE
+	base = MEMBASE;
+#else
 	base = 0;
+#endif
 
 	magic[0] = 0x00000005; /* appsbl */
 	magic[1] = 0x00000002; /* nand */