[ARM] pxa/em-x270: fix compile failure when CONFIG_APM_EMULATION=n

If CONFIG_APM_EMULATION=n em-x270 build fails with linker error:

arch/arm/mach-pxa/built-in.o: In function `em_x270_battery_critical': em-x270.c:(.text+0x12c0): undefined reference to `apm_queue_event'
arch/arm/mach-pxa/built-in.o: In function `em_x270_battery_low': em-x270.c:(.text+0x12c8): undefined reference to `apm_queue_event'
make: *** [.tmp_vmlinux1] Error 1

Fix it.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>