add recovery and kernel changes

Change-Id: If3df3e1c286559bec15b0fab084941c939272b83
Make the kernel image format parametric instead of a chain of if/elses

Change-Id: I54bfcdecb8647f7bcf744e72b2de19fcf4e4e7ac
kernel: Ignore errors with module building

Let kernel fully disable loadable modules

Change-Id: Ia37ec927b092c041ee4c68bf9fd0f28b7339c8ca
build: use the system's ccache by default

ccache 3.x supports direct mode (http://ccache.samba.org/manual.html#_the_direct_mode)
This is not supported in the prebuilt version.
Direct mode has been shown to decrease build time compared to the ccache in prebuilts

Note: this will require your cache to be recreated

PS3:
  make it so you need to export USE_SYSTEM_CCACHE=1 to use system ccache
  allow custom CCACHE_BASEDIR
oldChange-Id: Ib146011a3330637c2d306d329fcb39cea058ff12

Conflicts:
	core/combo/select.mk

Change-Id: Iee698ee4caf46a73986b748dc38709023416da1f
Remove prebuilt apk check