ART: Rework quick entrypoint code in Mir2Lir, cleanup

To reduce the complexity of calling trampolines in generic code,
introduce an enumeration for entrypoints. Introduce a header that lists
the entrypoint enum and exposes a templatized method that translates an
enum value to the corresponding thread offset value.

Call helpers are rewritten to have an enum parameter instead of the
thread offset. Also rewrite LoadHelper and GenConversionCall this way.
It is now LoadHelper's duty to select the right thread offset size.

Introduce InvokeTrampoline virtual method to Mir2Lir. This allows to
further simplify the call helpers, as well as make OpThreadMem specific
to X86 only (removed from Mir2Lir).

Make GenInlinedCharAt virtual, move a copy to X86 backend, and simplify
both copies. Remove LoadBaseIndexedDisp and OpRegMem from Mir2Lir, as they
are now specific to X86 only.

Remove StoreBaseIndexedDisp from Mir2Lir, as it was only ever used in the
X86 backend.

Remove OpTlsCmp from Mir2Lir, as it was only ever used in the X86 backend.

Remove OpLea from Mir2Lir, as it was only ever defined in the X86 backend.

Remove GenImmedCheck from Mir2Lir as it was neither used nor implemented.

Change-Id: If0a6182288c5d57653e3979bf547840a4c47626e
29 files changed