arm/imx: explicitly includes mach/hardware.h in pm-imx27.c

The pm-imx27.c references a number of things requiring the explicit
inclusion of mach/hardware.h.  Otherwise, when indirect inclusion
to mach/hardware.h gets cleaned up, we will see the following
compile error.

  CC      arch/arm/mach-imx/pm-imx27.o
arch/arm/mach-imx/pm-imx27.c: In function ‘mx27_suspend_enter’:
arch/arm/mach-imx/pm-imx27.c:22:3: error: implicit declaration of function ‘IOMEM’
arch/arm/mach-imx/pm-imx27.c:22:3: error: implicit declaration of function ‘IMX_IO_P2V’
arch/arm/mach-imx/pm-imx27.c: In function ‘mx27_pm_init’:
arch/arm/mach-imx/pm-imx27.c:42:2: error: implicit declaration of function ‘cpu_is_mx27’

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>