MPC8308RDB: minimal support for devboard from Freescale

This patch provides support for MPC8308RDB development board from
Freescale with a minimal set of features:
 Dual UART is supported
 NOR flash is supported
 Both TSEC Ethernet controllers are supported
 PCI Express initialization is supported

The following features are enabled in configuration but not fully tested:
 I2C (used to get the board revision)
 I2C-connected RTC
 VSC7385 switch

There is one (hopefully) minor issue: on soft reset the board sometimes
resets twice. I've not managed to find the fix for this problem yet.
As a workaround instruction cache can be disabled.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
diff --git a/boards.cfg b/boards.cfg
index da31c36..c23696f 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -331,6 +331,7 @@
 RPXsuper	powerpc	mpc8260		rpxsuper
 rsdproto	powerpc	mpc8260
 MPC8266ADS	powerpc	mpc8260		mpc8266ads	freescale
+MPC8308RDB	powerpc	mpc83xx		mpc8308rdb	freescale
 MPC8323ERDB	powerpc	mpc83xx		mpc8323erdb	freescale
 MPC8349EMDS	powerpc	mpc83xx		mpc8349emds	freescale
 MPC837XERDB	powerpc	mpc83xx		mpc837xerdb	freescale