Add i.MX6 and Xilinx to GENERIC.

Merge in the missing devices from the IMX6 and ZEDBOARD kernel configs. The
Freescale sdma device has been renamed to fslsdma to mark it as a platform
specific driver.

Reviewed by: ian
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D11564