net: lwm2m: add max device power source config option
net: lwm2m: add max device power source config option

The code in the LwM2M "Device" object was checking for this max
power source config value, except that it was never added as a
Kconfig option.  Let's go ahead and add it so apps can set the
value appropriately.

Signed-off-by: Michael Scott <17b9e1c64588c7fa6419b4d29dc1f4426279ba01@opensourcefoundries.com>

GiulianoFranchetto/zephyr,ldts/zephyr,mbolivar/zephyr,zephyriot/zephyr,galak/zephyr,nashif/zephyr,punitvara/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyriot/zephyr,explora26/zephyr,punitvara/zephyr,Vudentz/zephyr,ldts/zephyr,explora26/zephyr,punitvara/zephyr,mbolivar/zephyr,punitvara/zephyr,Vudentz/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,Vudentz/zephyr,Vudentz/zephyr,ldts/zephyr,Vudentz/zephyr,kraj/zephyr,finikorg/zephyr,explora26/zephyr,explora26/zephyr,zephyriot/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,mbolivar/zephyr,zephyriot/zephyr,punitvara/zephyr,nashif/zephyr,nashif/zephyr,zephyriot/zephyr,explora26/zephyr,ldts/zephyr,kraj/zephyr,nashif/zephyr,finikorg/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr