soc: qcom: hab: add the buffer size sanity check for exporting a buffer

hab only supports multiple page size memory export, so the exported buffer
size must be N * PAGE_SIZE w/ N > 0.

Change-Id: I0b59639b3ca8842ccd49deb6b32f29f68da0b7a4
Signed-off-by: Yao Jiang <yaojia@codeaurora.org>