community/qemu: explicitly enable libusb support
libusb is already an explicit dependency of the aport. However, according to the buildlog it is presently not autodetected:
libusb: NO
usb net redir: NO
OpenGL support: YES
GBM: YES
For this reason, libusb support is presently not enabled in Alpine's
QEMU version. This commit fixes this by explicitly passing the
--enable-libusb
flag to the configure script.