F3 bootloader: separate library_bl.mk

The PiOS source files are not needed for the bootloader
so this drops that dependency.
F4 bootloader: separate library_bl.mk

The PiOS source files are not needed for the bootloader
so this drops that dependency.
F3 Firmware: use library_fw.mk

This moves the common definitions into library.mk and the fw
specific source files to a library_fw.mk
F3 library_bl.mk: use common library.mk for shared defs
F4 Firmware: use library_fw.mk

This moves the common definitions into library.mk and the fw
specific source files to a library_fw.mk
F4 library_bl.mk: use common library.mk for shared defs
F3 BL: add required files to library.mk
F4 BL: add required files to library.mk
F3 BL: move the required files into F3 bl makefile

No need for a library_bl.mk file that is only included into one
makefile.  Just adds clutter and spread things around.
F4 BL: move the required files into F4 bl makefile

No need for a library_bl.mk file that is only included into one
makefile.  Just adds clutter and spread things around.
BL Makefiles: get rid of redundant settings

These settings also came from library.mk
F3 BU: use library.mk where appropriate
F4 BU: use library.mk where appropriate
BU/BL: remove more redundant cruft
Merge pull request #835 from peabody124/bl_dependencies

Bl dependencies