Fix graphics composer denial.

Right now, the hwcomposer hidl hal is unable to figure out where
to get the hidl mapper implementation.

It is expected that all graphics composer objects will need this
permission. The interfaces are written to work together with the
"IMapper" being the same-process ("sphal") component and the
"IComposer" interface being the binderized compoenent.

10-09 00:24:38.900   457   457 E SELinux : avc:  denied  { find } for
interface=android.hardware.graphics.mapper::IMapper pid=495
scontext=u:r:hal_graphics_composer_default:s0
tcontext=u:object_r:hal_graphics_mapper_hwservice:s0 tclass=hwservice_manager

Test: boot marlin, denial no longer present.
Bug: 38415912
Change-Id: I1b274be10e115fa7b53fb81e85be8827da05997e