RFR: JDK-8238851: Shenandoah: C1: Resolve into registers of correct type

[Roman Kennke]

In ShBSC1::ensure_in_register() we are blindly creating registers of
type T_OBJECT, even though in some cases we actually need T_ADDRESS.
This blows up when we verify oop registers: when the argument is of type
T_OBJECT we perform extra checks that fail when the value in register is
not actually an object.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8238851
Webrev:
http://cr.openjdk.java.net/~rkennke/JDK-8238851/webrev.01/
Testing: the provided testcase passes now. hotspot_gc_shenandoah

Ok?

Thanks,
Roman