transition to openocd from st-flash

[mcudev]

openocd is solid and this removes dependency on another tool, st-flash.

Tested:

make openocd STLINKv21=1
make flash STLINKv21=1
make flash_erase STLINKv21=1
make flash_boardloader STLINKv21=1
make flash_bootloader STLINKv21=1
make flash_firmware STLINKv21=1
make combine flash_combine STLINKv21=1

[mcudev]

Any chance this'll get pulled in? If not, I'll close it. Thanks!

[prusnak]

Don't close please. I am on vacation. The PR looks fine at first sight, will review later.

[mcudev]

Just rebased onto master and is again merge-able :)

[prusnak]

Please don't remove comments starting with ##. They are used to print help using make help.

[prusnak]

Also is -H in call to sudo necessary?

[mcudev]

I just put the comments back.

The -H allows pip cache to be used. Otherwise, you get a warning message that caching fails and it recommends to use -H. It works both ways. This way has cleaner screen output.

[prusnak]

Looks nice. Thanks!