FS#9281 Rename of splash functions.

FS#9281 Rename of splash functions.
* Remove gui_splash()
* Rename gui_syncsplash() to splashf() and remove its voice
capabilities.
* Rename the internal splash() to splash_internal() and introduce an
externally visible splash() that handles simple splashing  without
printf functionality e.g. splash(HZ, ID2P(LANG_FOO)); or splash(HZ,
"foo"); if a LANG_* id is passed it will be voiced.
* Adjust all places that called gui_syncsplash() to use the correct
variant from above.
* Export both new functions to plugins and adjust places calling
rb->splash() to use the correct variant so that we now have naming
consistency between the core and plugins.
* Fix one latent bug that would cause my sim to crash with the above
changes and correct P2STR and P2ID macros, thanks to pondlife.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@18282 a1c6a512-1295-4272-9138-f99709370657