soc/mediatek: Add SOF extended manifest to link

SOF needs this information for rimage to work, it contains data needed
by the kernel loader and not firmware per se.  Note that contra other
SOF platforms, this leaves the data in the live firmware image so it
can be inspected at runtime.  That's not needed by core SOF code, but
is handy for debugging.  And these devices have a ton of DRAM space
available.

Signed-off-by: Andy Ross <andyross@google.com>