Convert Android.mk to Android.bp for vendor snapshot.

This change enables the converted modules to be included
in the vendor snapshot, which considers only
soong-defined modules.

Conversion of the modules in this directory to
Android.bp was blocked by a build-time conditional check
of TARGET_ENABLE_MEDIADRM_64. Using a Soong config
variable, we can perform the conversion.

Bug: 161571531
Bug: 123557988
Test: Build with TARGET_ENABLE_MEDIADRM_64 :=
Test: Build with TARGET_ENABLE_MEDIADRM_64 := true
Test: Insepction of out/soong/soong.variables for each
Test: Inspection of target files package for each
Test: Verify inclusion of modules in vendor snapshot
Change-Id: I47c3b739dfafdf619f8a9a85de560652966af290