provide libstagefright_foundation_vendor to vendors

libstagefright_foundation_vendor is a vendor-only variant of the
libstagefright_foundation. Vendor libs and other VNDK libs should link
against this _vendor.so library. This vendor-only variant does not have
dependency to libpowermanager which is not available to vendors.

Headers are moved from the global include dir to module-local include
dir. This is because global include dir (e.g. frameworks/av/include) is
not provided when building with BOARD_VNDK_VERSION=current. Instead the
headers are exported via the module's export_include_dirs directive.

Short summary on the directory movement:

"some" libstagefright headers are moved from libstagefright/include to
libstagefright/include/media/stagefright. This is because the headers
are included as <media/stagefright/HEADER_NAME,h>.

libstagefrigut_foundation headers are moved from
libstagefright/include/foundation to
libstagefright/foundation/include/media/stagefright/foundation. Again
this is because the headers are included as
<media/stagefright/foundation/HEADER_NAME.h>.

Furthermore, in order to prevent sudden breakage, symlinks to the
module-local header directories are added to the global include
directory.

frameworks/av/include/media/stagefright ->
<libstagefright>/include/media/stagefright

frameworks/av/include/media/stagefright/foundation ->
<libstagefright_foundation>/include/media/stagefright/foundation

Bug: 37462569
Test: sailfish builds and boots
Test: BOARD_VNDK_VERSION=current m libstagefright_foundation_vendor is
successful

Merged-Id: Iadfa594e885e0bd39837ccb282993d3ba5b62852
Change-Id: Iadfa594e885e0bd39837ccb282993d3ba5b62852
(cherry picked from commit 093f0b7a)