ANDROID: staging: android: ion: Expose total heap and pool sizes via sysfs

Add sysfs attributes to track ion total heap and pool memory allocations.
The following sysfs attributes are added:

/sys/kernel/ion/total_heaps_kb
/sys/kernel/ion/total_pools_kb

Bug: 138148041
Bug: 154238995
Test: adb shell cat /sys/kernel/ion/*
Change-Id: If92770dc3389af865c619525f04d3ba0e013b244
Signed-off-by: Suren Baghdasaryan <surenb@google.com>