The rp2040 can be flashed without sudo when using udev rules to give the
user permission, but in a standard configuration sudo is required.
Here we make it possible for flash_usb to use sudo for the rp2040
target, and make it the default when using `make flash` for the rp2040.
As for other targets, one can set `NOSUDO=1` to not call through sudo.
Signed-off-by: Lasse Dalegaard <dalegaard@gmail.com>
a7b01857f5