Add entry m28evk to fix the following mxs build breakage.
  CHK     include/generated/compile.h
  CC      arch/arm/mach-mxs/clock-mx28.o
arch/arm/mach-mxs/clock-mx28.c: In function 'clk_misc_init':
arch/arm/mach-mxs/clock-mx28.c:748: error: implicit declaration of
function 'machine_is_m28evk'
make[1]: *** [arch/arm/mach-mxs/clock-mx28.o] Error 1
make: *** [arch/arm/mach-mxs] Error 2
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
 thales_adc             MACH_THALES_ADC         THALES_ADC              3492
 ubisys_p9d_evp         MACH_UBISYS_P9D_EVP     UBISYS_P9D_EVP          3493
 atdgp318               MACH_ATDGP318           ATDGP318                3494
+m28evk                 MACH_M28EVK             M28EVK                  3613
 smdk4212               MACH_SMDK4212           SMDK4212                3638
 smdk4412               MACH_SMDK4412           SMDK4412                3765