msm: pcie: update debugfs feature

This change adds 4 new entries to pci_msm directory in debug:
 - base_sel: the base address.
 - wr_offset: the register's offset.
 - wr_mask: the bit(s) to mask.
 - wr_value: the value to write to the register.

This change also adds two new debugfs features.
 - specify a register and write a value to it.
 - specify a base and dump all its registers.
 - add the counter for link on/off

Change-Id: Ife29a72496457c9807bcb01f13008abc282bb81d
Signed-off-by: Tony Truong <truong@codeaurora.org>