spimaster: mosi should be held high when not transmitting.
spi: reset counter on idle.
debugger: load filesz bytes.

For something like .bss it will occupy lots of space in the target
address space but perhaps not the file.  Avoid copying bytes we don't
need to.
rtl/execute: fix BLTE implementation.

This was checking the wrong flags and not taking the branch when it
should.
rtl/sim: order branch tests the same in both the rtl and simulation.
bootrom: increase to 16KB.

In preparation for SD card bootloading where we need to parse FAT.
bootrom: add an SD bootrom.

The bootrom now looks on SPI CS 0 for an SD card.  It parses the MBR to
find the active partition and then looks for a file in the top level
called BOOT.ELF.  This is loaded into memory and executed.
rtl/sim: implement carry as not-carry.

This is like ARM does and we can use the same condition predicates.
oldland-test: remove sim specific bootroms.

They can all use the same bootrom now.
travis: require gcc-oldland.

The bootrom now requires a C compiler.