pcie: tegra: dynamic link speed & clock setting

pcie: tegra: dynamic link speed & clock setting

Based on the capability of card, we should dynamically
set the mselect, pciex clock and link speed selection.
Clocks will be set to support the highest capable card
This patch:
1. enable the clocks to minimal value during boot
2. Based on card capability, it boosts the clocks
3. And train the link

Bug 1483608

Change-Id: Iaf90f9b06846f8e23e4f60d1670a1db9ec562257
Signed-off-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-on: http://git-master/r/437560
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Eric Brower <ebrower@nvidia.com>
Reviewed-by: Vidya Sagar <vidyas@nvidia.com>
Reviewed-by: Venkat Moganty <vmoganty@nvidia.com>