MONITOR_SAVE: make use of the m65common framework

[gurcei]

@bubbob42 reported some problems compiling the monitor_save tool for mac here:

• https://discord.com/channels/719326990221574164/805492126128930846/805501814744416297

gcc -Wall -g -std=gnu99 -I/opt/local/include -L/opt/local/lib -I/usr/local/include/libusb-1.0 -L/usr/local/lib -mno-sse3 -march=x86-64 -o bin/monitor_save src/tools/monitor_save.c
src/tools/monitor_save.c:347:25: error: use of undeclared identifier 'B2000000'
    if (cfsetospeed(&t, B2000000)) perror("Failed to set output baud rate");
                        ^
src/tools/monitor_save.c:348:25: error: use of undeclared identifier 'B2000000'
    if (cfsetispeed(&t, B2000000)) perror("Failed to set input baud rate");
                        ^
src/tools/monitor_save.c:350:25: error: use of undeclared identifier 'B4000000'
    if (cfsetospeed(&t, B4000000)) perror("Failed to set output baud rate");
                        ^
src/tools/monitor_save.c:351:25: error: use of undeclared identifier 'B4000000'
    if (cfsetispeed(&t, B4000000)) perror("Failed to set input baud rate");
                        ^
4 errors generated.
make: *** [bin/monitor_save] Error 1

Seems like Paul feels this is a tool we should keep and make it use the m65common framework, so as to avoid such errors that were due to this old tool not using Paul's workaround to get higher serial-bps on Mac os-x, a workaround that already exists within the m65common library.

[lydon42]

I might be already looking at this in my refactor-m65 branch.