layers: Use real enum value for alignment checks in device_limits

Previously this used '1'.

Also clean up the enum, and description of device_limits checks.

Found by inspection while reviewing #290.

Change-Id: I710d9b8fad0ca027eb3de67b6c2c70b5628af5a5
Signed-off-by: Chris Forbes <chrisforbes@google.com>
3 files changed