Merge tristan's patch:

Merge tristan's patch:
while compiling with GCC I have found two issues in PcatPciRootBridge.c:

* when vendor id is read, the code read 2 * 2 bytes into a buffer of 2 bytes.
  The 'buffer overflow' crashed efi.

* when pci configuration header is read, the code read by chunks of 4 bytes,
  but the buffer is aligned on 2 bytes.  According to the compilation options,
  the reads may fail (and the failure is ignored).

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@7602 6f19259b-4bc3-4df7-8a09-765794883524