Use trampolines for calls to helpers

This is an ARM specific optimization to the compiler
that uses trampoline islands to make calls to runtime
helper functions.  The intention is to reduce the size
of the generated code (by 2 bytes per call) without
affecting performance.

By default this is on when generating an OAT file.  It is
off when compiling to memory.

To switch this off in dex2oat, use the command line option:
--no-helper-trampolines

Enhances disassembler to print the trampoline entry on the
BL instruction like this:

0xb6a850c0: f7ffff9e  bl      -196 (0xb6a85000)  ; pTestSuspend

Bug: 12607709
Change-Id: I9202bdb7cf21252ad807bd48701f1f6ce8e3d0fe