A long time ago, Android.mk in devices had the same semantics
as the current AndroidBoard.mk. This eventually caused problems
(as it didn't allow having a true Android.mk there) so we switched,
and left an error behind in case people were still using the old
semantics (i.e. having an Android.mk but no AndroidBoard.mk).
Fast forward a few years to the present: we're finding that we want
to get rid of AndroidBoard.mk, so there are devices that will have
Android.mk but not AndroidBoard.mk. As this is becoming a legitimate
case, the error for it is removed, and the include for AndroidBoard.mk
is made optional.
Change-Id: Ic683419d4aaab122259715e0112660d2a6359e91
Non-HTC devices may have multiple files constituting their "radio
image". Generalize the INSTALLED_RADIOIMAGE_TARGET variable a bit:
initially define it as empty, then let AndroidBoard.mk files add to
it. Provide a convenience function add-radio-image for them to call
to add files. Put all those files into the target_files zip for use
in OTA and fastboot package construction.
Note that for HTC devices, this changes the name of the radio image in
the target_files zip: instead of "RADIO/image" it will be
"RADIO/radio.img". Tools that use the target_files zip will need to
be changed.
