MAINTAINERS: Update maintainer for USB xHCI

As discussed with Marek, this adds myself as the maintainer to
offload the USB xHCI part.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/doc/git-mailrc b/doc/git-mailrc
index 556db0a..5a365cd 100644
--- a/doc/git-mailrc
+++ b/doc/git-mailrc
@@ -133,6 +133,7 @@
 alias spmi           uboot, mateusz
 alias ubi            uboot, hs
 alias usb            uboot, marex
+alias xhci           uboot, bmeng
 alias video          uboot, ag
 alias patman         uboot, sjg
 alias buildman       uboot, sjg