netmap-modules: make deterministic builds for drivers

The driver builds are optional, but for deterministic builds,
we should should be able to explicitly enable/disable the
builds for them in a proper place (maybe in BSP).
But we can't use PACKAGECONFIG since there is no option for
each driver, and the options are:
 --no-drivers    do not compile any driver
 --no-drivers=   do not compile the given drivers (comma sep.)
 --drivers=      only compile the given drivers (comma sep.)

So use NETMAP_DRIVERS to list the needed drivers and add proper
configs to EXTRA_OECONF, the default is no drivers, and all
supported drivers are listed in NETMAP_ALL_DRIVERS.

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>