[POWERPC] 85xx: rework platform Kconfig

* Allow multiple boards to be selected in a single build
* Removed Kconfig option '85xx' which existed only for compat with arch/ppc
* Added a multiplatform 85xx defconfig (mpc85xx_defconfig). This builds
  all 85xx boards except sbc8560 and stx_gp3 since these to boards have
  board specific ifdef in driver code that may break all other boards

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 9af05a2..8f3f04d 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -2301,7 +2301,7 @@
 
 config GIANFAR
 	tristate "Gianfar Ethernet"
-	depends on 85xx || 83xx || PPC_86xx
+	depends on FSL_SOC
 	select PHYLIB
 	select CRC32
 	help