Kconfig: Sketch out 'board' kconfiguration

Provision how boards shall be configured into the build system by way of
kconfig.

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
src/drivers: Kconfig'ify driver build subsystem

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
src/common: Kconfig'ify common build subsystem

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>