init.rc: set initial cpuset to all cores

Starting zygote early requires cpuset to be initialized to all cores for
foreground cpuset. Change to expolit all cores by default at boot and
let device manufacturers override to proper values in device specific
init script.

Bug: 36576280
Test: marlin boot fast and checked cpuset during early boot
Change-Id: I2c1ce0630e58a7b04d1a453c6740d3f0bce9de9f
(cherry picked from commit 2e83b86a)