[RFC] implement syscall pciconfig_iobase

[Zhang Le <r0bertz@gentoo.org>]

This is for xorg-server support.

Currently, xorg-server on loongson need a patch:
http://www.gentoo-cn.org/gitweb/?p=loongson;a=blob;f=x11-base/xorg-server/files/xorg-server-1.5.3-loongson.patch;h=9c48b3752b7f14b6603524f46ae832f312e7c6fe;hb=HEAD#l37
Please note that line 37, the last parameter to mmap, which is the ioBase_phys,
is hardcoded.

This patch no long applies to xorg-server git master.
So I took at look at the code trying to find out why. And then I found powerpc
has implemented this syscall: pciconfig_iobase

Please take a look at the following code:
http://cgit.freedesktop.org/xorg/xserver/tree/hw/xfree86/os-support/linux/lnx_video.c#n517

At the first glance, it is absolutely a good idea to implement this for mips,
too. However when I read pciconfig_iobase's manpage, I found this sentence:

       Most  of  the interaction with PCI devices is already handled by the
       kernel PCI layer, and thus these calls should not normally need to be
       accessed from userspace.

So I decided to bring this issue here, so that you guys could give me some
advice.

Thanks in advance!

Zhang, Le