hexagon: drop empty and unused free_initrd_mem

hexagon: drop empty and unused free_initrd_mem

hexagon never reserves or initializes initrd and the only mention of it is
the empty free_initrd_mem() function.

As we have a generic implementation of free_initrd_mem(), there is no need
to define an empty stub for the hexagon implementation and it can be
dropped.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Rapoport <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Richard Kuo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>