Generate info on revision and datetime

To have an info about when it was generated, add the git revision (if
not from stdio) and datetime info to the header.
Add multicore registers
Whitespace fixes
Make compatible with assembler code

When gcc is used to compile assembler code it does not understand the
integer literal suffix ('U'). Add a macro OR1K_UNSIGNED(x) that adds
the suffix when __ASSEMBLER__ is not set.
Merge pull request #2 from wallento/master

A few small changes