m/n/b/fwprune: adapt to fsspec and use

This modifies the fwprune tool to generate fsspecs instead of making
copies and makes it take a list of paths for suffix matching instead
of a directory as input. It also adds the fsspec_linux_firmware rule
which uses the utility to actually build a partial fsspec. Finally it
integrates the linux-firmware external repository and uses that rule
to ship firmware in Metropolis.

Change-Id: I0552995105eda84e63d7259040ad36d794079308
Reviewed-on: https://review.monogon.dev/c/monogon/+/534
Reviewed-by: Mateusz Zalega <mateusz@monogon.tech>
diff --git a/WORKSPACE b/WORKSPACE
index b27e651..f6b1155 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -137,6 +137,13 @@
     version = "5.15.2",
 )
 
+load("//third_party/linux-firmware:external.bzl", "linux_firmware_external")
+
+linux_firmware_external(
+    name = "linux-firmware",
+    version = "20211216",
+)
+
 load("//third_party/edk2:external.bzl", "edk2_external")
 
 edk2_external(name = "edk2")