Request for review (L): 6797305: Add LoadUB and LoadUI opcode class

[Christian Thalinger]

http://cr.openjdk.java.net/~twisti/6797305/webrev.00/

Here is the (almost) final version of my unsigned load changes.  I added
enc_class functions for all load instructions on x86_32 and x86_64.
Should I do the same for sparc too?

-- Christian