Add total size of DMA-BUFs exported to 'dumpsys meminfo'

When ION support is not detected, print the total size of DMA-BUFs
exported as part of dumpsys meminfo.

Bug: 167709539
Test: dumpsys meminfo
Change-Id: I3439a8f00cf1aef37e5043b505ed53d47a8a4756
Merged-In: I3439a8f00cf1aef37e5043b505ed53d47a8a4756