phy: ti: am654: update PCIe serdes config

Update PCIe serdes config to latest suggested for
hardware. This fixes cases of failure to enumerate
in Gen2 mode with some cards.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Link: https://lore.kernel.org/r/20200727194603.44636-4-nsekhar@ti.com


[fix typo threshold]
Signed-off-by: Vinod Koul <vkoul@kernel.org>