classes/recipes: Switch to use inherit_defer

Now that bitbake supports the use of inherit_defer, switch all conditional
(variable based) inherits to use this instead. This leads to more a more
deterministic user experience since there is no longer an immediate expansion
and later changes to the variables in question (e.g. a bbappend) are
accounted for.

This patch tries to ensure the behaviour before/after remains as unchanged
as it reasonably can, e.g. by always inherting populate_sdk_base. native
and nativesdk continue to need to be inherited last, hence being used
with inherit_defer in a handful of very specific cases.

(From OE-Core rev: 451363438d38bd4552d5bcec4a92332f5819a5d4)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-recipe/kernel.bbclass

@@ -171,7 +171,7 @@ set -e
 # image types.
 
 KERNEL_CLASSES ?= " kernel-uimage "
-inherit ${KERNEL_CLASSES}
+inherit_defer ${KERNEL_CLASSES}
 
 # Old style kernels may set ${S} = ${WORKDIR}/git for example
 # We need to move these over to STAGING_KERNEL_DIR. We can't just