The driver for MediaTek gen3 PCIe hosts de-asserts all reset
signals at the same time using a single register write operation.
Delay the de-assertion of the #PERST signal by 100ms as some PCIe
devices fail to come up otherwise.
Sync from https://github.com/immortalwrt/immortalwrt/commit/6a2e17d5c1
1b99cd51c5