libui: use uint64_t in dump and getTotalSize to avoid overflow issues

Fixes add-overflow errors caught by ubsan when running AHardwareBuffer
VK tests.

Test: dEQP-VK.api.external.memory.android_hardware_buffer.image_formats#r16g16b16a16_sfloat
Change-Id: I9ce1c9ee5f972a95a97de88a47d84982a99359c5
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>