Add ":sphal" as required in apex_manifest.json

mediaswcodec binary requires "sphal" linker namespace at runtime.
Previously, the dependency was hard-coded in linkerconfig itself.
With ":sphal" declared as required in apex_manifest, linkerconfig can
handle swcodec APEX  without hard-coded APEX name.

Q-Compatibility:
- "requireNativeLibs" key in the apex_manifest is stripped out. When the
APEX is installed in Q system, ld.config.txt in the apex will be used.

R-Compatibility:
- ":sphal" is silently ignored by linkerconfig in R. But because
linkerconfig in R hard-coded the dependency to "sphal" namespace, it
will work correctly.

Bug: 162456867
Test: build & device boots
Change-Id: Ibc0e0eee46762dac2825f2ff4c2cf6dcbeaea320