package/pkg-golang: new package infrastructure

package/pkg-golang: new package infrastructure

This patch adds a new infrastructure for golang based packages.

Signed-off-by: Angelo Compagnucci <angelo@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[Arnout:
 - Rewrap comments to 80 columns.
 - Create a global definition of GO_TARGET_ENV.
 - <PKG>_GO_ENV is appended to the default env instead of replacing it.
 - Add a note to inner-golang-package that only target is supported.
]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>