No error code are available to signal an invalid firmware content.
Drivers that can check the firmware content validity can not return this
specific failure to the user-space

Expand the firmware error code with an additional code:
- "firmware invalid" code which can be used when the provided firmware
  is invalid

Sync lib/test_firmware.c file accordingly.
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20231122-feature_firmware_error_code-v3-1-04ec753afb71@bootlin.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>