msm: secure_buffer: Increase size of QCOM_SECURE_MEM_SIZE

We are seeing cases where QCOM_SECURE_MEM_SIZE is not large enough to hyp
unassign large sg lists.
This is resulting in memory leaks since we can't return memory which
wasn't unassigned back to the kernel.

Messages such as the following will be seen in the kernel:
get_info_list_from_table: Not enough memory allocated.

Increase the size of QCOM_SECURE_MEM_SIZE to 2MB to accommodate these new
use cases.
In the future we should look into breaking up these sg lists to save
memory.

Change-Id: Ib30c8d46d8090b1cb7199779512b8e666924f379
Signed-off-by: Liam Mark <lmark@codeaurora.org>