PCI: qcom: Limit TLP size to 2K to work around hardware issue

Limit TLP size to 2K to work around a hardware bug in the v0 version of
PCIe IP.  When using default TLP size of 4K, the internal buffer gets
corrupted due to this hardware bug.

This bug was originally noticed during ssh session between APQ8064-based
board and PC.  Network packets got corrupted randomly and terminated the ssh
session due to this bug.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>