usb: rockchip: implement skeleton for K_FW_GET_CHIP_VER command

Chip Version is a string saved in BOOTROM address space Little Endian.

Ex for rk3288: 0x33323041 0x32303134 0x30383133 0x56323030
which brings:  320A20140813V200

Note that memory version do invert MSB/LSB so printing the char
buffer would show: A02341023180002V

Signed-off-by: Alberto Panizzo <alberto@amarulasolutions.com>