ART: Add 16-bit Thumb2 ROR, NEGS and CMP for high registers.

Also clean up the usage of set_cc flag. Define a SetCc
enumeration that specifies whether to set or keep condition
codes or whether we don't care and a 16-bit instruction
should be selected if one exists.

This reduces the size of Nexus 5 boot.oat by 44KiB (when
compiled with Optimizing which is not the default yet).

Change-Id: I047072dc197ea678bf2019c01bcb28943fa9b604