sys-kernel/linux-firmware: New snapshot, add USE flags.

sys-kernel/linux-firmware: New snapshot, add USE flags.

Introduce two USE flags:
"redistributable": Install all firmware files whose license will at
least allow redistribution. (So, USE="-redistributable" will install
only files that are free software.) This is enabled by an IUSE default.
"unknown-license": In addition, install firmware files with an unknown
license according to upstream's WHENCE file.

In savedconfig code, call rm only once, instead of executing it for
each file.

EAPI bumped to 7.

Added without KEYWORDS for testing.

Bug: https://bugs.gentoo.org/318841#c20
Package-Manager: Portage-2.3.66, Repoman-2.3.12
Signed-off-by: Ulrich Müller <ulm@gentoo.org>