Add support for cortex-a73.

Bug: 37647380

Test: Built target with cortex-a73 for both 32 bit/64 bit.
Test: Built target with cortex-a53.cortex-a57 for both 32 bit/64 bit.
Test: Ran bionic unit tests, ran art target tests.

(cherry picked from commit 6fca047b)

Change-Id: I2c48e1bc7f4a3c4548d1c66f87eab19c8618a0b8