mkefidisk: Always use rootwait and document kernel parameters used

mkefidisk: Always use rootwait and document kernel parameters used

Without a reliable way of knowing if the target device with be an
asyncronous block device on the target (MMC or USB), err on the side of
caution of always specifcy "rootwait", ensuring the kernel will wait for
the device to appear and not abort if it hasn't appeared in time for
mount.

Document the remaining kernel parameters added by this script on the
same line as rootwait.

(From OE-Core rev: 5b6a6a3872fd341cf978be40c69707223e3c29df)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>