Added command line hooking option ...

compiler, linker, assembler and binary command lines can now be modified
using the hooks mechanism. Also, '--any_placement=first_fit' linker option
is now used only on LPC4088 using this mechanism, in order to preserve
compatibility with the other targets.

Added toolchain hooks and support for LPC4088_EA binary generation ...

A new hooks mechanism (hooks.py) allows various targets to customize
part(s) of the build process. This was implemented to allow generation of
custom binary images for the EA LPC4088 target, but it should be generic
enough to allow other such customizations in the future. For now, only the
'binary' step is hooked in toolchains/arm.py.