pci: access to specific bits via sysfs

pci: access to specific bits via sysfs

Enabling 'Extended Tag' and resetting 'Max Read Request Size' in PCI
config space have big impacts to i40e performance. They cannot be
changed on some BIOS implementations, though can on others. Two sys
files of 'extended_tag' and 'max_read_request_size' are added to
support changing them by 'echo' in user space.

Signed-off-by: Helin Zhang <helin.zhang@intel.com>
Signed-off-by: Jing Chen <jing.d.chen@intel.com>
Acked-by: Cunming Liang <cunming.liang@intel.com>
Acked-by: Jijiang Liu <jijiang.liu@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: Heqing Zhu <heqing.zhu@intel.com>
Tested-by: Waterman Cao <waterman.cao@intel.com>