linux-firmware: move i915 firmware symlinks to WHENCE

There's a handful of firmware symlinks in the i915 firmware
directory, move the creation of these to the WHENCE file.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
CC: José Roberto de Souza <jose.souza@intel.com>
CC: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
CC: Anusha Srivatsa <anusha.srivatsa@intel.com>
CC: Rodrigo Vivi <rodrigo.vivi@intel.com>
CC: Tom O'Rourke <Tom.O'Rourke@intel.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>