uboot: Cleaning up bootargs for prowl

 - Build bootarg contents in code, matching behaviour
of prowl/chimera
 - Add gfactive parameter to detect current partition

Matching change to ginstall: go/fibercl/79567
Removing hardcoded kernel cmdline: go/fibercl/79590

In reference to b/31805455, b/31805037

Change-Id: If9e3afd8499371ceb2d4ef69645fa2108b6933b8
1 file changed