[media] V4L: add missing EXPORT_SYMBOL* statements to vb2

videobuf2-memops and videobuf2-core can be compiled as modules, in which
case 3 more symbols from videobuf2-memops.c have to be exported.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/videobuf2-memops.c

@@ -77,6 +77,7 @@ void vb2_put_vma(struct vm_area_struct *vma)
 
 	kfree(vma);
 }
+EXPORT_SYMBOL_GPL(vb2_put_vma);
 
 /**
  * vb2_get_contig_userptr() - lock physically contiguous userspace mapped memory
@@ -141,6 +142,7 @@ done:
 	up_read(&mm->mmap_sem);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(vb2_get_contig_userptr);
 
 /**
  * vb2_mmap_pfn_range() - map physical pages to userspace
@@ -180,6 +182,7 @@ int vb2_mmap_pfn_range(struct vm_area_struct *vma, unsigned long paddr,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(vb2_mmap_pfn_range);
 
 /**
  * vb2_common_vm_open() - increase refcount of the vma