malta: Allow MIPS64 builds

Both real Malta boards & emulators that mimic Malta (eg. QEMU) can
support MIPS64 CPUs. Allow MIPS64 builds of U-Boot for such boards,
which enables the user to make use of the whole 64 bit address space.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
diff --git a/board/imgtec/malta/Kconfig b/board/imgtec/malta/Kconfig
index 2bb8e8b..98eb4d1 100644
--- a/board/imgtec/malta/Kconfig
+++ b/board/imgtec/malta/Kconfig
@@ -10,6 +10,7 @@
 	default "malta"
 
 config SYS_TEXT_BASE
-	default 0xbe000000
+	default 0xbe000000 if 32BIT
+	default 0xffffffffbe000000 if 64BIT
 
 endif