RFR(S) 8166869: [JVMCI] record metadata relocations for metadata references

[Tom Rodriguez]

http://cr.openjdk.java.net/~never/8166869/webrev
https://bugs.openjdk.java.net/browse/JDK-8166869

JVMCI records metadata references in the metadata section, so scanning of referenced metadata will work properly but it never actually creates a relocation in code or constants section. This means the disassembly is a little less readable than it might be.  This adds the creation of the appropriate relocation.  Tested by inspection of assembly printing on sparc and x86.

tom