meminfo: Add ReadVmallocInfo()

This is to replace occurrences of get_allocated_vmalloc_memory().
Splitting into libmeminfo already found a bug with current code which
failed to account for memory allocated by modules due to addition of
the extra [%module_name%] in __builtin_return_address().

  See: https://elixir.bootlin.com/linux/latest/source/kernel/kallsyms.c#L373



Also improves the performance a bit in the process.

Bug: 119639955
Bug: 111694435
Test: libmeminfo_test 1 --gtest_filter=SysMemInfoParser.TestVmallocInfo
Test: libmeminfo_benchmark --benchmark_filter=BM_VmallocInfo_*
Result:
----------------------------------------------------------------
Benchmark                         Time           CPU Iterations
----------------------------------------------------------------
BM_VmallocInfo_old_fixed     459239 ns     457268 ns       1532
BM_VmallocInfo_new           386032 ns     384353 ns       1821
----------------------------------------------------------------

Change-Id: I1b6606ac73b5cc2dac31d24487b462ec9abfb2ef
Signed-off-by: Sandeep Patil <sspatil@google.com>