ti814x_evm: Switch to SYS_GENERIC_BOARD

Take over maintainership as well.  Not tested as PG2.0 (which I have)
needs additional work over PG1.0 (which Matt has).

Cc: Matt Porter <mporter@konsulko.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>