Add start/end LPRAM symbols.  We might need to use the _elpram symbol if we want to add some LPRAM to heap

SAMD21: Add build framework for DMA support.  Nothing there yet except for skeletal logic taken from SAM3/4.

SAML21: Since SERCOM5 usese a different output channel, it will also need a different GCLK generator

Lincoln60: Add a thttpd-binfs configuration.  That configuration still does not work on initial commit