libaudiohal: statically link HAL 7.x interface libraries

Since the interface libraries are not actually shared
with HAL services—the system has their own versions
under /system, while the HAL uses the versions from /vendor,
there are no gains from using them as shared libraries.
Switching to static linking allows better optimization
of duplicate and unused code by the linker and reduces
memory usage. For example, audioserver memory use on redfin,
as reported by dumpsys meminfo (in Kilobytes):

7.0 shared libs: TOTAL PSS: 14360, RSS: 28544
7.1 shared libs: TOTAL PSS: 15515, RSS: 29120
7.1 static libs: TOTAL PSS: 14997, RSS: 28336

These interface libraries are not used by any other module on
the system partition. This is confirmed by the fact that after
this change their .so files do not present anymore on the system
partition, which means no other module depends on them.

Bug: 219730472
Test: adb shell dumpsys meminfo <audioserver PID>
Change-Id: Ic590560e5e9646a173427046a53fca6d7f9f2a10