lmkd: Change procfs read routine to handle files larger than 1 page in size

Files like /proc/zoneinfo or /proc/<pid>/status can be larger than 4KB
page size. Change reread_file routine to resize read buffer whenever
it is not big enough to read the entire file. Start with 1-page buffer
and double its size until it's big enough to read the entire file.
Read /proc/zoneinfo during initialization to initialize the buffer
to a big enough size and avoid re-allocations when under memory pressure.

Bug: 137010962
Test: lmkd_unit_test
Change-Id: If9a5b0d27c2f4de9063f0fd0f36f908ece87dcce
Signed-off-by: Suren Baghdasaryan <surenb@google.com>