powerpc: mpc8260: consolidate CONFIG_MPC8260 and CONFIG_8260

Before this commit, CONFIG_MPC8260 and CONFIG_8260
were used mixed-up.

All boards with mpc8260 cpu defined both of them:
  - CONFIG_MPC8260 was defined in board config headers
      and include/common.h
  - CONFIG_8260 was defined arch/powerpc/cpu/mpc8260/config.mk

We do not need to have both of them.
This commit keeps only CONFIG_MPC8260.

This commit does:
 - Delete CONFIG_8260 and CONFIG_MPC8260 definition
   in config headers and include/common.h
 - Rename CONFIG_8260 to CONFIG_MPC8260
    in arch/powerpc/cpu/mpc8260/config.mk.
 - Rename #ifdef CONFIG_8260 to #ifdef CONFIG_MPC8260

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Wolfgang Denk <wd@denx.de>
diff --git a/examples/standalone/Makefile b/examples/standalone/Makefile
index 7e0e5b7..9ab5446 100644
--- a/examples/standalone/Makefile
+++ b/examples/standalone/Makefile
@@ -11,7 +11,7 @@
 extra-$(CONFIG_SPI_FLASH_ATMEL)    += atmel_df_pow2
 extra-$(CONFIG_MPC5xxx)            += interrupt
 extra-$(CONFIG_8xx)                += test_burst timer
-extra-$(CONFIG_8260)               += mem_to_mem_idma2intr
+extra-$(CONFIG_MPC8260)            += mem_to_mem_idma2intr
 extra-$(CONFIG_PPC)                += sched
 
 #