fix: systick delay

feat: vos0, system clock at 480 MHz

few minorities

chore: split main functions

fix: ability to change pll vcosel, disable pll outputs

feat: implement fmc sdram control

feat: implement clocks enabling

fix: unicode strings

feat: implement cdc application layer, fix enumeration

fix: usb should not rewrite DIEPCTL bits

feat: add rx data callback, increase tx fifo size

fix: make queue thread safe

fix: ensure register access are inline

fix: correctly send functional descriptor

The functional descriptor was not sent correctly,
specifically, it was pointed to its address,
instead of the pointer itself. That meant bunch
of irrelevant stuff was sent instead.

feat: use task_result to indicate blocking

There should be no spin loops inside of the
interrupts, so this change removes them,
and instead uses a result system that has
WOULD_BLOCK result. When this result is returned,
it is expected there was no side-effect and the
function can safely be reran later.

feat: implement enumeration fully

chore: update pin, exti, delay

fix: fifo has to be volatile

docs: add documentation comments to most functions

feat: implement usb devicd cdc descriptors, init, setup