allmodconfig is broken by the addition of the -mcpu=cortex-a9
flag for smc.S:

arch/arm/mach-tango/smc.S:1:0: warning: switch -mcpu=cortex-a9 conflicts with -march=armv6k switch

This sets the flag in the same way that all other platforms
do, to fix the compile error.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>