msm: pcie: enable/disable PCIe AER from debugfs

PCIe Advanced Error Reporting is currently enabled
by default with no way of disabling it. AER is not
always ideal to have enabled as it may flood PCIe
IPC logs. Thus, this change provides an option to
enable and disable AER from debugfs.

Change-Id: Ic5b90ad47b4d97ad492745c1f57e1ab85236772a
Signed-off-by: Tony Truong <truong@codeaurora.org>