pcie: shell: Add dump and BDF string arguments

Add argument dump for dumping first 16 PCI configuration space
registers same way lspci -x is doing. Also parse bdf string as
argument. pcie can be called following way:

  uart:~$ pcie 0:1f.4
   ...
  uart:~$ pcie 0:1f.4 dump
   ...

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>