UART0 Initialization, uMon image preparation for non-XIP device booting, and some cleanup

[Jarielle Catbagan]

These series of patches (patches 1 through 8) adds the necessary tasks to initialize UART0, builds
an MLO file from a GP header and a uMon image for booting from non-XIP devices, and cleans up
some of the source files in the BBB port.