usb: Add environment based device ignorelist

Add the environment variable "usb_ignorelist" to prevent USB devices
listed in it from being bound to drivers. This allows to ignore devices
which are undesirable or trigger bugs in u-boot's USB stack.
Devices emulating keyboards are one example of undesirable devices as
u-boot currently supports only a single USB keyboard device. Most
commonly, people run into this with Yubikeys, so let's ignore those in
the default environment.

Based on previous USB keyboard specific patches for the same purpose.

Link: https://lore.kernel.org/u-boot/7ab604fb-0fec-4f5e-8708-7a3a7e2cb568@denx.de/
Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Janne Grunau <j@jannau.net>

doc/usage/environment.rst

@@ -366,6 +366,19 @@ tftpwindowsize
     This means the count of blocks we can receive before
     sending ack to server.
 
+usb_ignorelist
+    Ignore USB devices to prevent binding them to an USB device driver. This can
+    be used to ignore devices are for some reason undesirable or causes crashes
+    u-boot's USB stack.
+    An example for undesired behavior is the keyboard emulation of security keys
+    like Yubikeys. U-boot currently supports only a single USB keyboard device
+    so try to probe an useful keyboard device. The default environment blocks
+    Yubico devices as common devices emulating keyboards.
+    Devices are matched by idVendor and idProduct. The variable contains a comma
+    separated list of idVendor:idProduct pairs as hexadecimal numbers joined
+    by a colon. '*' functions as a wildcard for idProduct to block all devices
+    with the specified idVendor.
+
 vlan
     When set to a value < 4095 the traffic over
     Ethernet is encapsulated/received over 802.1q