dt-bindings: PCI: hisi: Delete the obsolete HiSilicon PCIe file

The hisilicon-pcie.txt file is no longer useful since commit
c2fa6cf7 (PCI: dwc: hisi: Remove non-ECAM HiSilicon
hip05/hip06 driver), so delete it and remove related code in
MAINTAINERS file.

Suggested-by: Zhou Wang <wangzhou1@hisilicon.com>
Link: https://lore.kernel.org/r/1617111799-109749-1-git-send-email-liudongdong3@huawei.com


Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Krzysztof Wilczyński <kw@linux.com>