emulator: 64-bit kernel for 32-bit arm image

Starting in P, all 32-bit and 64-bit architectures use 64-bit
binder interface. This is similar to ag/3582011 for x86.

Bug: 71861550
Test: lunch sdk_phone_armv7-userdebug; m -j; emulator
Change-Id: I152a89ba46e81f27bde0e166cb224d2a740fc989
Merged-In: I152a89ba46e81f27bde0e166cb224d2a740fc989
(cherry picked from commit 50df6f59)