PowerPC: Update MIP405/MIP405T to use Kconfig better

Convert CONFIG_MIP405T from SYS_EXTRA_OPTIONS to a real config

There are two boards, MIP405 and MIP405T that have a few differences.
Start by checking for CONFIG_TARGET_MIP405.  Then introduce
CONFIG_TARGET_MIP405T and use that not CONFIG_MIP405T.  Next, convert
also convert the usage of CONFIG_ISO_STRING to be based on Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/mpl/pati/pati.h b/board/mpl/pati/pati.h
index 2600bba..2938056 100644
--- a/board/mpl/pati/pati.h
+++ b/board/mpl/pati/pati.h
@@ -201,7 +201,7 @@
 #define PCI_VENDOR_ID_MPL	0x18E6
 #define PCI_DEVICE_ID_PATI	0x00DA
 
-#if defined(CONFIG_MIP405)
+#if defined(CONFIG_TARGET_MIP405) || defined(CONFIG_TARGET_MIP405T)
 #define PATI_FIRMWARE_START_OFFSET	0x00300000
 #define PATI_ISO_STRING  "MEV-10084-001"
 #endif