PCI: aardvark: Move PCIe reset card code to advk_pcie_train_link()

Move code which belongs to link training (delays and resets) into
advk_pcie_train_link() function, so everything related to link training,
including timings is at one place.

After experiments it can be observed that link training in aardvark
hardware is very sensitive to timings and delays, so it is a good idea to
have this code at the same place as link training calls.

This patch does not change behavior of aardvark initialization.

Link: https://lore.kernel.org/r/20200907111038.5811-6-pali@kernel.org
Tested-by: Marek Behún <marek.behun@nic.cz>
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>