soc: xtensa: esp32: Add CONFIG_SMP protection
soc: xtensa: esp32: Add CONFIG_SMP protection

Add #ifdef CONFIG_SMP around code that only needs to exist when
SMP is enabled.

Also include ksched.h to get decleration of z_sched_ipi.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@intel.com>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr