grub/xhci: rename to grub/xhci_nvme

we have the "default" tree, then the "nvme" tree which adds
nvme support.

the "xhci" tree adds xhci patches, *and* nvme patches.

riku suggested that i rename it accordingly, and his advice
was quite correct, indeed wise.

this will reduce confusion for contributors, including *myself*.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/grub/xhci_nvme/patches/0015-usb-Add-enum-for-xHCI.patch

@@ -0,0 +1,29 @@
+From 260f27e1ea1dbcdeb63d4411dbdddb97ebb39668 Mon Sep 17 00:00:00 2001
+From: Patrick Rudolph <patrick.rudolph@9elements.com>
+Date: Mon, 7 Dec 2020 08:41:22 +0100
+Subject: [PATCH 15/26] usb: Add enum for xHCI
+
+Will be used in future patches.
+
+Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
+---
+ include/grub/usb.h | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/include/grub/usb.h b/include/grub/usb.h
+index 688c11f6d..ea6ee8c2c 100644
+--- a/include/grub/usb.h
++++ b/include/grub/usb.h
+@@ -51,7 +51,8 @@ typedef enum
+     GRUB_USB_SPEED_NONE,
+     GRUB_USB_SPEED_LOW,
+     GRUB_USB_SPEED_FULL,
+-    GRUB_USB_SPEED_HIGH
++    GRUB_USB_SPEED_HIGH,
++    GRUB_USB_SPEED_SUPER
+   } grub_usb_speed_t;
+ 
+ typedef int (*grub_usb_iterate_hook_t) (grub_usb_device_t dev, void *data);
+-- 
+2.39.5
+