qseecom: Update the name for a param in device tree

RPM handles the crypto clocks, going forward this could
be handled by some other sub-systems as well, so change the name to
be generic. Also, update the same param in the documentation file.

Change-Id: I62f6bdecc2d6f5987aedacce6eaa66e741c6d855
Signed-off-by: Hariprasad Dhalinarasimha <hnamgund@codeaurora.org>