ARM64: Fix disassembly of branch targets.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/225743004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20543 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fixed flooring division by -1 on ARM.

We should avoid ASR #0 on ARM. Simplified and improved code a bit
while we're there on all platforms. Human brains are very bad at
understanding nested structures...

BUG=v8:3259
LOG=y
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/227553003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20544 ce2b1a6d-e550-0410-aec6-3dcde31c8c00