soc: qcom: hvc: add missing x7 argument to the 32bit __hvc stub

__hvc should take 11 arguments instead of 10. Add the missing x7
argument to avoid compilation error if the driver gets enabled on
32bit targets.

Change-Id: I09985235fdbfb64e81743a71ceb2764c32d3a3b1
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>