doc: Document tentative protocol for erase and write commands

Subject to change in the future. This is not the final version.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
libqiprog: Add calls for setting write/erase commands

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
libqiprog: Add QIPROG_ERR_LARGE_ARG error code

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_master: Implement set_erase_size call

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_master: Implement set_erase_command call

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_master: Implement set_custom_erase_command call

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_master: Implement set_write_command call

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_master: Implement set_custom_write_command call

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
usb_dev: Connect erase/write commands to device drivers

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
libqiprog: Add definitions for erase flags

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>