travis: Split and rename xilinx ARM in to two jobs

Split the ARMv7 and AArch64 platforms into separate jobs, to avoid them
taking too long to build overall.  Also rename them from "Xilinx" to
"Zynq*" to reflect slightly better what is being built and to pull in a
few more board matches.

Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Tom Rini <trini@konsulko.com>