Change build config of libldac from Android.mk to Android.bp

* In an effort to modernize build configurations to the new Soong
  system, we need to upgrade existing Android.mk files to Android.bp
* This file is done through "androidmk Android.mk > Android.bp"
* Soong does not support Makefile flags from BoardConfig.mk and hence
  ifeq ($(BUILD_LDAC_32BIT_FIXED_POINT_), TRUE) is not supported and
  has to be removed
* Since the flag is not used by any BoardConfig.mk yet (always FALSE)
  the removal is safe
* This flag is specific to devices without an FPU such as ARM Cortex-R
  series and external 32-bit DSPs

Bug: 32958753
Test: Code compilation, no user visible effects
Change-Id: I33ee7767dd21ad7e055fbad42a5874cdb2069f07