atomisp: remove indirection from sh_css_malloc

We have one hard coded set of behaviour so unpick the indirection and function
pointers. This isn't the whole story. A lot of the callers are known sizes and
use cases so we can switch them directly to kmalloc later on.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>