dmaengine: idxd: Change license on idxd.h to LGPL

mainline inclusion
from mainline-v5.14
commit 25905f60
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I596WO


CVE: NA

Intel-SIG: commit 25905f60 dmaengine: idxd: Change license on idxd.h to LGPL.
Incremental backporting patches for DSA/IAA on Intel Xeon platform.

--------------------------------

This file was given GPL-2.0 license. But LGPL-2.1 makes more sense
as it needs to be used by libraries outside of the kernel source tree.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>