Only import allocationSize for a fuchsia buffer

This has 2 advantages:
1) The importer can be certain the size of the imported memory is at
least what was asked for, so texture reads can't go outside it.
2) We can commit a smaller amount of a larger VMO, which can save time
and increase flexibility.

MA-498
Test: nuc:go/magma-tps#L2

Change-Id: I51392746f69a201fbb3c6f5f6779e0d8f28e2961
1 file changed