Adapt the four PrintInt method for RV64

[privat]

Added:

• PrintInt and PrintIntUnsigned handle the long register values in RV64 mode
• PrintIntHex and PrintIntBinary also add more leading digits in RV64 mode

Implementation note:

• For signed representation (PrintInt), Long.toString (since Java8) can handle both RV32 and RV64.
• The three other syscalls rely on an unsigned representation, it's simpler to have an if and use the correct int or long version.

Tests are also added