RTC non volatile storage support

configname: CONFIG_RTC_NVMEM

Linux Kernel Configuration
└─>Device Drivers
└─>Real Time Clock
└─>RTC non volatile storage support
In linux kernel since version 4.2 (release Date: 2015-08-30)  
Say yes here to add support for the non volatile (often battery
backed) storage present on RTCs.

selects
CONFIG_NVMEM