qseecom: make change to support sg list entry number larger than 512

qseecom_send_modfd_cmd_64 converts non-contiguous ION memory fd to
scatter-gather physical address list, and supports up to 512 SG list
entries. Now, 512 is not enough if client wants to send large data
in a fragmented system. In this change, if SG list entry number is
larger than 512, we will allocate a new contiguous kernel buffer,
then save all SG entries into this new buffer.

Change-Id: Id90eefb98b63bf16db755dae8e1482e448090f47
Signed-off-by: Zhen Kong <zkong@codeaurora.org>