usb_modeswitch: update to 1.2.4

This patch updates usb_modeswitch to version 1.2.4. The
usb_modeswitch.mk needed to be modified for usb_modeswitch to compile.
Also added extra remove section for the added help scripts and files.

[thomas.petazzoni@free-electrons.com:
  bumped further to 1.2.4 instead of 1.2.3, adjusted the patch accordingly
  use TARGET_CONFIGURE_OPTS instead of passing CC, LD manually
  add license information.]

Signed-off-by: J.C. Woltz <jwoltz@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>