firmware: Remove embedding of multiple images in one module.
this patch removes possibility of embedding more than one firmware image in one kernel module through the parent reference in the firmware_register() function.
This patch is a preparation for firmware subsystem modification for moving firmware images from kernel modules to userland.
The mechanism is not used and it can be functionally fully replaced by putting each firmware image in its own module.
Removing the functionality significantly simplifies handling of firmware images. If firmware images are moved to userland the logical grouping of modules could be expressed by putting the related firmware images into one directory if needed.