classes: add bbclass phyexternalsrc
classes: add bbclass phyexternalsrc

This is a fork of the externalsrc bbclass of poky. Its main purpose is
to assist in barebox and kernel development. It behaves quite
differently than the poky class. It will execute all tasks but filters
all remote sources from the SRC_URI. Any patches found locally will
still apply. To use it, you have to add the following lines to your
local.conf, e.g. for the linux-ti kernel:

INHERIT += "phyexternalsrc"
EXTERNALSRC_pn-linux-ti = "${HOME}/yocto/sources/linux-ti"

More details can be found in the class header.

Signed-off-by: Stefan Müller-Klieser <a3e08e35e4a42be768e7d0e76ae1ba321c2a66dd@phytec.de>

PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec