Backport changes from Galileo implementation
Add EFI stage loader

EFI expects position independent code. That won't work well for RIOT, so
the stage loader takes the ELF blob, copies it into the right place, and
executes the entry code.
[WIP] add Intel Galileo board
Dump
Dump [paging works!]
Move 8250 into optional driver
Dump
Dump
Fixes