staging: r8188eu: move local definitions into rtw_fw.h

Move some defines and the definition of struct rt_firmware_hdr
from rtw_fw.h to rtw_fw.c. These definitions are used only by
the fw layer.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220206161809.423031-7-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>