msm: pcie: add support for configuring Gen4 PCIe core preset

For chipsets which are Gen4 capable, the PCIe core preset
settings need to be configured accordingly based on trace
length. Therefore add the support to configure PCIe core
preset.

Change-Id: I6968e24135482aa356dd94fde4988ef342747337
Signed-off-by: Tony Truong <truong@codeaurora.org>