android: make libdrm*.so available to the vendor partition

android: make libdrm*.so available to the vendor partition

libdrm_<vendor>.so are moved to the vendor partition (/vendor/lib or
/system/vendor/lib if there is no dedicated vendor partition), since
they are vendor-specific extension that must not be in the system
partition which should be generic.

libdrm.so (which is generic) is built/installed twice: once to
/vendor/lib to satisfy the dependency for the libdrm_<vendor>.so libs
and once to /system/lib for platform clients such as the recovery
executable.

The platform variant of libdrm is named as libdrm_platform.so since
in Android.mk we can't have two different shared libs having
same soname. In the near future, this will be fixed by converting these
Android.mk files to Android.bp and mark the module libdrm as
'vendor_available: true'. (See
https://android-review.googlesource.com/c/368372/ for further detail on
the property)

Signed-off-by: Jiyong Park <jiyong@google.com>