build: Add alternate recovery to pathmap

Change-Id: I2827ace9729b6af8d5b4e637374ccd1e5902dd55
Fix the alternate recovery inclusion logic

Change-Id: Ifb59d61dae44dd639d7f891dc57bb326b06b1118
build: Include pre-pathmap extra config

 * We need to mess with the pathmap for building simplerecovery in user
   builds, but previously there was no way to do this externally.
 * Source an optional config file before loading the pathmap so that we
   can do some magic without having to set environment variables outside
   the normal build system.

Change-Id: I6132f9e6ffa04678378a5a00ba37b98cd4d9f773
Revert "inline kernel dtb build"

This reverts commit 8609a0fb59fa3d943cd33137b0910ced41013102.
This is specific to a device (or vendor) and is confusing people
building for other 8974s. A more generic implementation is required,
and until then device-local mkbootimg overloads can/should be
used.

Change-Id: Ia582f9ca73d454da4ada894b489aea883d6f5186

Conflicts:
	core/tasks/kernel.mk
Make the kernel image format parametric instead of a chain of if/elses

Change-Id: I54bfcdecb8647f7bcf744e72b2de19fcf4e4e7ac

Conflicts:
	core/tasks/kernel.mk
Don't make assumptions about the formats of build descriptions

Change-Id: Id83a7594e9e1b9b4ffbdbaba695506d8d0d21a46