staging: mt7621-pci: rewrite pcie phy related functions

Function 'bypass_pipe_rst' and 'set_phy_for_ssc' can be
written in a cleaner way. Instead of use comments to see which
bits are the ones which are being enabled add new macros with
that information using BIT and GENMASK kernel macros. Avoid the
use of set_pcie_phy which is kind of dark and use new macros also
resetting and adding bits using bitwise operators directly in the
code. Now these function are offset-based on the port to use them
cleaner in driver probe functio and improving readability.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>