kernel: bump 5.15 to 5.15.138

kernel: bump 5.15 to 5.15.138

Changelog: https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.15.138

Removed upstreamed:
	generic/backport-5.15/819-v6.6-0018-nvmem-imx-correct-nregs-for-i.MX6SLL.patch[1]
	generic/backport-5.15/819-v6.6-0019-nvmem-imx-correct-nregs-for-i.MX6UL.patch[2]
	generic/backport-5.15/819-v6.6-0020-nvmem-imx-correct-nregs-for-i.MX6ULL.patch[3]

All other patches automatically rebased.

1. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.15.138&id=6e22bf6f00d593b0a7e0b2f418fde89317424671
2. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.15.138&id=6efd498009b987a92f57f3bdae476f0503364fb7
3. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.15.138&id=6e22bf6f00d593b0a7e0b2f418fde89317424671

Build system: x86_64
Build-tested: ramips/tplink_archer-a6-v3
Run-tested: ramips/tplink_archer-a6-v3

Signed-off-by: John Audia <therealgraysky@proton.me>
[Refreshed on top of OpenWrt 23.05]
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 573c8c3d78cdf494156f763c7182c0f16a8d7263)