tools: Small improvement to print_memory_map script ...

This patch:
- Add the __COHERENT_RAM_START__ and __COHERENT_RAM_END__ symbols.
- Improve how the symbols are found with a regex.
- Add a build option to revert the memory layout output.

Change-Id: I54ec660261431bc98d78acb0f80e3d95bc5397ac
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>

tools: Add show_memory script ...

show_memory is a simple tools that parse the blx.map files and print a
representation of the memory layout for the latest build.
This representation is based on standard symbols present on the map
files as: __TEXT_START/END__, __RODATA_START/END__, __STACKS_START/END__
, etc..

Change-Id: Iba3e301a1a9fee9a35abf1afdb69093617d33929
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>