* device/arm: add system timer registers
Add SYST registers and bit definitions to device/arm.
Add a setup function.
Add an example that uses it to blink an LED.
This change results in changes to all smoketests for Cortex-M based
chips: they get a bit smaller (32-48 bytes). I'm not sure why but
probably because the inliner made a different inlining decision. There
was a similar effect when files generated from SVD files switched to the
new volatile types so it's probably harmless.
This is very useful for debugging. It differentiates between a stack
overflow and other errors (because it's easy to see when a stack
overflow occurs) and prints the old stack pointer and program counter if
available.
This is one step towards removing unnecessary special casts in most
cases. It is also part of removing as much magic as possible from the
compiler (the pragma is explicit, the special name is not).
Don't store addresses in the values of registers, this leads to problems
with char arrays (among others). Instead, do it like it's done in C with
raw addresses cast to struct pointers.
This commit also splits gen-device.py, as AVR and ARM have very
different ideas of what a register is. It's easier to just keep them
separate.
