ARM: pxa: work around duplicate definition of GPIO24_SSP1_SFRM

The symbol "GPIO24_SSP1_SFRM" is defined in both mfp-pxa27x.h and
mfp-pxa25x.h. Since the macro is not actually used in the cm-x2xx.c
file, but it includes both headers, a safe workaround should be
to just undefine it from the .c file. This is a bit hacky and
the headers should be fixed to not both define it, but for now
it gets us around an annoying warning.

Without this patch, building cm_x2xx_defconfig results in:

In file included from arch/arm/mach-pxa/include/mach-pxa/pxa27x.h:7:0,
                 from arch/arm/mach-pxa/cm-x2xx.c:25:
arch/arm/mach-pxa/include/mach-pxa/mfp-pxa27x.h:215:0: warning: "GPIO24_SSP1_SFRM" redefined [enabled by default]
arch/arm/mach-pxa/include/mach-pxa/mfp-pxa25x.h:111:0: note: this is the location of the previous definition

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: Mike Rapoport <mike@compulab.co.il>