LWIS: Implement memory allocator for reuse

Memory is allocated/deallocated at each IOCTL, transaction, etc.,
which could be a very costly operation. LWIS should have a memory
allocator to help reuse memory buffer to reduce the number to
allocations.

Bug: 199428848
Test: GCA, CTS
Signed-off-by: Holmes Chou <holmeschou@google.com>
Change-Id: Ibd52cdf8974e18fc2855ec7883b2815f3cf0b966