m68k: sun3: Improve Sun3/3x DVMA abstraction in <asm/dvma.h>

When building with W=1:

arch/m68k/sun3/dvma.c:65:13: warning: no previous prototype for ‘sun3_dvma_init’ [-Wmissing-prototypes]
65 | void __init sun3_dvma_init(void)
| ^~~~~~~~~~~~~~

arch/m68k/sun3x/dvma.c:178:6: warning: no previous prototype for ‘dvma_unmap_iommu’ [-Wmissing-prototypes]
179 | void dvma_unmap_iommu(unsigned long baddr, int len)
| ^~~~~~~~~~~~~~~~

Fix this by moving the declarations for sun3_dvma_init() and
dvma_unmap_iommu() to <asm/dvma.h>. Avoid #ifdefs in callers by
providing dummy static inline functions.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/m68k/include/asm/dvma.h

···
 #define dvma_vtob(x) dvma_vtop(x)
 #define dvma_btov(x) dvma_ptov(x)
 
+void sun3_dvma_init(void);
+
 static inline int dvma_map_cpu(unsigned long kaddr, unsigned long vaddr,
 			       int len)
 {
 	return 0;
 }
+
+static inline void dvma_unmap_iommu(unsigned long baddr, int len) { }
 
 #else /* Sun3x */
 
···
 #define dvma_vtob(x) ((unsigned long)(x) & 0x00ffffff)
 #define dvma_btov(x) ((unsigned long)(x) | 0xff000000)
 
-extern int dvma_map_cpu(unsigned long kaddr, unsigned long vaddr, int len);
+static inline void sun3_dvma_init(void) { }
 
+int dvma_map_cpu(unsigned long kaddr, unsigned long vaddr, int len);
 
+void dvma_unmap_iommu(unsigned long baddr, int len);
 
 /* everything below this line is specific to dma used for the onboard
    ESP scsi on sun3x */

arch/m68k/sun3/sun3dvma.c

···
 
 #undef DVMA_DEBUG
 
-#ifdef CONFIG_SUN3X
-extern void dvma_unmap_iommu(unsigned long baddr, int len);
-#else
-static inline void dvma_unmap_iommu(unsigned long a, int b)
-{
-}
-#endif
-
-#ifdef CONFIG_SUN3
-extern void sun3_dvma_init(void);
-#endif
-
 static unsigned long *iommu_use;
 
 #define dvma_index(baddr) ((baddr - DVMA_START) >> DVMA_PAGE_SHIFT)
···
 
 	dvma_unmap_iommu(DVMA_START, DVMA_SIZE);
 
-#ifdef CONFIG_SUN3
 	sun3_dvma_init();
-#endif
-
 }
 
 unsigned long dvma_map_align(unsigned long kaddr, int len, int align)