Support for 64-bit counters in ARC HS38 cores

configname: CONFIG_ARC_TIMERS_64BIT

Linux Kernel Configuration
└─>Device Drivers
└─>Clock Source drivers
└─>Support for 64-bit counters in ARC HS38 cores
In linux kernel since version 4.1 (release Date: 2015-06-21)  
This enables 2 different 64-bit timers: RTC (for UP) and GFRC (for SMP)
RTC is implemented inside the core, while GFRC sits outside the core in
ARConnect IP block. Driver automatically picks one of them for clocksource
as appropriate.