[platform][zynq] fix uart driver
[platform][zynq] initialize more of the uart

no longer relies on the target specific jam table except for
baud rate calculations.
[platform][zynq] update clock setting api, print boot reason
[scripts] add travis-build.sh and .travis.yml file

Github provides travis continuous integration service. This change makes
it possible to utilize travis with prebuilt toolchains. The build matrix
is defined in .travis.yml file.