Dynamically load device-specific recovery UI lib.

We used to statically link the device-specific recovery UI extension
(`TARGET_RECOVERY_UI_LIB`) into `recovery`. Such a logic can't be easily
migrated to Soong, as modules specified by `TARGET_RECOVERY_UI_LIB` may
not be built with Soong.

Instead of porting all the device-specific codes over, this CL builds
and installs the UI lib as a shared library with Android.mk. `recovery`
dlopen(3)'s and dlsym(3)'s `make_device` to invoke the device-specific
UI lib on start.

Note that in order to make dlopen(3) actually working, we have to switch
`recovery` to be dynamically linked (we will make the move later
anyway).

Bug: 110380063
Test: Build and boot into marlin recovery image. Check that
      device-specific recovery UI is successfully loaded.
Change-Id: Ia9861c7559a95f3f50676534540c0cb87cae4574