BACKPORT: FROMLIST: PCI: mediatek-gen3: Add MT8196 support

The MT8196 is an ARM platform SoC that has the same PCIe IP as the
MT8195.
However, it requires additional settings in the pextpcfg registers.
Introduce pextpcfg in PCIe driver for these settings.

Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
(am from https://patchwork.kernel.org/patch/13925177/)
(also found at https://lore.kernel.org/r/20250103060035.30688-3-jianjun.wang@mediatek.com

)

Conflicts:
   drivers/pci/controller/pcie-mediatek-gen3.c

BUG=b:383258443
TEST=build pass and boot to shell
UPSTREAM-TASK=b:379039276

Change-Id: I41c6b447d454c41b594fc1495ad4b1138fc3cbea
Signed-off-by: Hsin-Te Yuan <yuanhsinte@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/6174698


Reviewed-by: Fei Shao <fshao@chromium.org>
Commit-Queue: Fei Shao <fshao@chromium.org>
Tested-by: Fei Shao <fshao@chromium.org>
Signed-off-by: Hubert Mazur <hmazur@google.com>