system: Declare qemu_[min/max]rampagesize() in 'system/hostmem.h'

system: Declare qemu_[min/max]rampagesize() in 'system/hostmem.h'

Both qemu_minrampagesize() and qemu_maxrampagesize() are
related to host memory backends, having the following call
stack:

  qemu_minrampagesize()
     -> find_min_backend_pagesize()
         -> object_dynamic_cast(obj, TYPE_MEMORY_BACKEND)

  qemu_maxrampagesize()
     -> find_max_backend_pagesize()
        -> object_dynamic_cast(obj, TYPE_MEMORY_BACKEND)

Having TYPE_MEMORY_BACKEND defined in "system/hostmem.h":

  include/system/hostmem.h:23:#define TYPE_MEMORY_BACKEND "memory-backend"

Move their prototype declaration to "system/hostmem.h".

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20250308230917.18907-7-philmd@linaro.org>
Acked-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250311085743.21724-2-philmd@linaro.org
Signed-off-by: Cédric Le Goater <clg@redhat.com>