linux-raspberrypi: fix build with devtool
linux-raspberrypi: fix build with devtool

Currently, building linux-raspberrypi with "devtool build" breaks
because ${B}.config doesn't yet exist when do_configure_prepend runs.

Fix this by taking some logic from kernel.bbclass do_configure to populate
${B}.config before do_configure_prepend.

The full explanation for why this is necessary is fairly complex:

- In devtool builds, externalsrc.bbclass gets inherited and sets a list of
SRCTREECOVEREDTASKS, which don't get run because they affect the source tree
and, when using devtool, we want the developer's changes to be the single
source of truth. kernel-yocto.bbclass adds do_kernel_configme to
SRCTREECOVEREDTASKS, so it doesn't run in a devtool build., In a normal
non-devtool build, do_kernel_configme creates ${B}.config.

- Normally (e.g. in linux-yocto), it would be OK that do_kernel_configme
doesn't run, because the first few lines of do_configure in kernel.bbclass
populate ${B}.config from either ${S}.config (if it exists) for custom
developer changes, or otherwise from ${WORDIR}/defconfig.

- In linux-raspberrypi, we add do_configure_prepend, which tweaks
${B}.config. Since this runs *before* the kernel.bbclass do_configure,
${B}.config doesn't yet exist and we hit an error. Thus we need to move
the logic from do_configure up to before our do_configure_prepend. Because
we are copying only a portion of do_configure and not the whole thing,
there is no clean way to do it using OE functionality, so we just
copy-and-paste.

Signed-off-by: Martin Kelly <c87c89f8a4ed3f9815bf6eb199372979d459c1c8@xevo.com>

agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,kraj/meta-raspberrypi,kraj/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,schnitzeltony/meta-raspberrypi,kraj/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,agherzan/meta-raspberrypi