Add launcher grid spec for tablet

- Introduced device_category to allow grids to be only enabled for certain device types. By default grids are enabled for all device types, so old OEM device_profiles aren't affected
  - Removed device_profiles_split.xml as a result and merged with device_profiles.xml
- Added deviceType in InvariantDeviceProfile to replace isSplitDisplay and centralize the logic
- Only has 6x5 grid with new default layout that works better for tablets

Bug: 198575341
Test: manual
Change-Id: I03f6727ce837ffeee6321b6d7c53942338d0cf30