Fix Lost RAM calculation by accounting for ION mapped heaps

ION mapped heaps are not reflected in process PSS because ION driver
maps them using remap_pfn_range that sets VM_PFNMAP flag for each
mapped ION heap VMA and consequently excludes these VMAs from PSS
calculation. Change memory accounting to consider ION mapped heaps
as part of kernel used memory which fixes the Lost RAM calculation
that currently includes mapped ION heaps.

Bug: 155409819
Test: verify Lost RAM after opening camera app
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Merged-In: I2bad40bbe7d14b1c61534d661b612200ef1084e4
Change-Id: I2bad40bbe7d14b1c61534d661b612200ef1084e4