32MHz crystal support

currently I see there is no support for 32MHz crystal but I have module which is using 32MHz and I was trying to create a custom variant to support this by implementing the HCLK initialization in initVariant() but its called in main() after low freq clock init

logically I think initVariant() should be the first function to be executed which allows variant manager to initialize his/her board support before the generic common initialization.

Another approach will be to use the macro approach similar to lowfreq selection for generic nrf51 board settings.