MIPS: Move CONFIG_SYS_TEXT_BASE to Kconfig

Move CONFIG_SYS_TEXT_BASE to Kconfig, and add default values in board
Kconfig files matching what was present in their config headers. This
will make it cleaner to conditionalise the value for Malta based on 32
vs 64 bit builds.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
diff --git a/Kconfig b/Kconfig
index f53759a..4b46216 100644
--- a/Kconfig
+++ b/Kconfig
@@ -268,7 +268,7 @@
 
 config SYS_TEXT_BASE
 	depends on SPARC || ARC || X86 || ARCH_UNIPHIER || ARCH_ZYNQMP || \
-		(M68K && !TARGET_ASTRO_MCF5373L) || MICROBLAZE
+		(M68K && !TARGET_ASTRO_MCF5373L) || MICROBLAZE || MIPS
 	depends on !EFI_APP
 	hex "Text Base"
 	help