linux-firmware: rename packages for i915 firmware

linux-firmware: rename packages for i915 firmware

Change the package name from intel-igpu-firmware-* to i915-firmware-*,
the prefix "intel-igpu" is misleading, i915 firmware is not only for
iGPU but also for dGPU now.

Remove the redundant "intel" as i915 is already well known.

More accurate file classification to handle following files correctly:

  adlp_dmc.bin
  mtl_huc.bin
  mtl_huc_gsc.bin
  mtl_gsc_1.bin

The pattern in regex is "([[:alnum:]]+)_([[:alnum:]]+)(_[\w-.]+)?\.bin",
where $1 is the platform, $2 is the firmware type (dmc, guc, huc, etc.),
and the optional $3 which is revision or other suffix.

Glob first to narrow down the target file set, and then split with "_"
to extract the firmware type (remove the ".bin" in case there is no $3)

Add package "i915-firmware" as a meta package to install all the i915
firmwares, it is a balance between simplicity and optimization.

* Installing all the available firmwares as a whole, can support all the
  platforms, not only the current one but also the future ones. The
  price to pay is the increased size.
* If we want to minimize the storage, we can customize to install the
  necessary ones only, even for the target platform only (e.g. ADL) and
  skip the others. The price to pay is the time to tune.

What I am going to do is:

* Let drm-i915 driver depend on i915-firmware-dmc, which is small and
  can cover most of the old platforms
* Let the user select i915-firmware to install all the i915 firmwares as
  a whole to cover the latest or future platforms

Signed-off-by: Joe Zheng <joe.zheng@intel.com>
Link: https://github.com/openwrt/openwrt/pull/16276
Signed-off-by: Robert Marko <robimarko@gmail.com>