x86/defconfig: Enable CONFIG_USB_XHCI_HCD=y

A spanking new machine I just got has all but one USB ports wired as 3.0.
Booting defconfig resulted in no keyboard or mouse, which was pretty
uncool.  Let's enable that -- USB3 is ubiquitous rather than an oddity.
As 'y' not 'm' -- recovering from initrd problems needs a keyboard.

Also add it to the 32-bit defconfig.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-usb@vger.kernel.org
Link: http://lkml.kernel.org/r/20181009062803.4332-1-kilobyte@angband.pl
Signed-off-by: Ingo Molnar <mingo@kernel.org>