Prevent double-counting of kernel stack size in dumpsys reports

When kernel is configured with CONFIG_VMAP_STACK=y kernel stacks are mapped
into process space and therefore already accounted as part of the value
returned by ReadVmallocInfo and reported under MEMINFO_VM_ALLOC_USED
category. Introduce isVmapStack function to check if kernel is configured
with that option and if so do not exclude kernel stack size in the
calculation of memory used by kernel.

Bug: 146088882
Test: dumpsys meminfo with CONFIG_VMAP_STACK enabled and disabled
Change-Id: I9230bbf0ab05524cf52ded35171fd9ec3da16fa0
Signed-off-by: Suren Baghdasaryan <surenb@google.com>