soc: qcom: update config dependencies for QCOM_RPMPD

Since QCOM_RPMPD is bool and it depends on QCOM_SMD_RPM
which is tristate, configurations such as arm64:allmodconfig
result in

CONFIG_QCOM_RPMPD=y
CONFIG_QCOM_SMD_RPM=m

This in turn results in

drivers/soc/qcom/rpmpd.o: In function `rpmpd_send_corner':
rpmpd.c:(.text+0x10c): undefined reference to `qcom_rpm_smd_write'
drivers/soc/qcom/rpmpd.o: In function `rpmpd_power_on':
rpmpd.c:(.text+0x3b4): undefined reference to `qcom_rpm_smd_write'
drivers/soc/qcom/rpmpd.o: In function `rpmpd_power_off':
rpmpd.c:(.text+0x520): undefined reference to `qcom_rpm_smd_write'
make: *** [vmlinux] Error 1

Fix it by making QCOM_RPMPD depend on QCOM_SMD_RPM=y

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>