lmkd: Rename is_go_device variable to better reflect its function

Rename is_go_device variable to low_ram_device to better reflect
its meaning and relation to ro.config.low_ram variable.

Change-Id: I6e2eaebe79cf2e6edf861f7c602e52a5b573ad0a
Signed-off-by: Suren Baghdasaryan <surenb@google.com>