cpu/lpc2387: use the same default stack sizes as cortexm_common
cpu/lpc2387: use the same default stack sizes as cortexm_common

Both architectures are variants of the ARM architecture and use the same
toolchain.
There is no reason to have such wildly different defaults.

This results in some tests passing that would crash before:

 - [x] `tests/pkg_libcose`
 - [x] `tests/pkg_qdsa`
 - [x] `tests/pkg_relic`
 - [x] `tests/pkg_tweetnacl`
 - [x] `tests/pthread_tls`

`THREAD_EXTRA_STACKSIZE_PRINTF_FLOAT` is not used anywhere in RIOT
anymore, so just drop it.

miri64/RIOT,miri64/RIOT,OTAkeys/RIOT,yogo1212/RIOT,x3ro/RIOT,authmillenon/RIOT,authmillenon/RIOT,authmillenon/RIOT,ant9000/RIOT,yogo1212/RIOT,OlegHahm/RIOT,miri64/RIOT,authmillenon/RIOT,mtausig/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kYc0o/RIOT,toonst/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,toonst/RIOT,mtausig/RIOT,josephnoir/RIOT,ant9000/RIOT,josephnoir/RIOT,yogo1212/RIOT,OTAkeys/RIOT,yogo1212/RIOT,mtausig/RIOT,yogo1212/RIOT,toonst/RIOT,smlng/RIOT,basilfx/RIOT,basilfx/RIOT,jasonatran/RIOT,kaspar030/RIOT,kYc0o/RIOT,mtausig/RIOT,OlegHahm/RIOT,smlng/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kYc0o/RIOT,miri64/RIOT,toonst/RIOT,OTAkeys/RIOT,kaspar030/RIOT,ant9000/RIOT,basilfx/RIOT,smlng/RIOT,x3ro/RIOT,miri64/RIOT,ant9000/RIOT,authmillenon/RIOT,basilfx/RIOT,jasonatran/RIOT,x3ro/RIOT,OlegHahm/RIOT,kaspar030/RIOT,x3ro/RIOT,kYc0o/RIOT,josephnoir/RIOT,kYc0o/RIOT,OlegHahm/RIOT,josephnoir/RIOT,basilfx/RIOT,jasonatran/RIOT,kaspar030/RIOT,josephnoir/RIOT,toonst/RIOT,ant9000/RIOT,smlng/RIOT,x3ro/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,mtausig/RIOT,jasonatran/RIOT,smlng/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,jasonatran/RIOT