Bare metal port fixes

[mkurc-ant]

This PR fixes the bare-metal port plus adds some improvements:

• Bumped the core coremark submodule
• Do not force ITERATIONS in the build script
• Allow providing the following build parameters in the port makefile: ARCH (ISA), ABI, DEBUG and TICKS_PER_SEC
• Do not use custom printf implementation in favor of ee_printf from coremark. The latter has support for printing floats which is necessary to obtain the final coremark score value at the end of the program (when HAS_FLOAT is set).

[oharboe]

@jerryz123 FYI