cpuidle: Fix ARM_QCOM_SPM_CPUIDLE configuration

When CONFIG_ARM_QCOM_SPM_CPUIDLE is y and CONFIG_MMU is not set,
compiling errors are encountered as follows:

drivers/cpuidle/cpuidle-qcom-spm.o: In function `spm_dev_probe':
cpuidle-qcom-spm.c:(.text+0x140): undefined reference to `cpu_resume_arm'
cpuidle-qcom-spm.c:(.text+0x148): undefined reference to `cpu_resume_arm'

Note that cpu_resume_arm is defined when MMU is set. So, add dependency
on MMU in ARM_QCOM_SPM_CPUIDLE configuration.

Fixes: a871be6b ("cpuidle: Convert Qualcomm SPM driver to a generic CPUidle driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: He Ying <heying24@huawei.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210406123328.92904-1-heying24@huawei.com