asm-generic/page.h: Make pfn accessors static inlines

Making virt_to_pfn() a static inline taking a strongly typed
(const void *) makes the contract of a passing a pointer of that
type to the function explicit and exposes any misuse of the
macro virt_to_pfn() acting polymorphic and accepting many types
such as (void *), (unitptr_t) or (unsigned long) as arguments
without warnings.

For symmetry we do the same change for pfn_to_virt.

Immediately define virt_to_pfn and pfn_to_virt to the static
inline after the static inline since this style of defining
functions is used for the generic helpers.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/asm-generic/page.h

@@ -74,8 +74,16 @@ extern unsigned long memory_end;
 #define __va(x) ((void *)((unsigned long) (x)))
 #define __pa(x) ((unsigned long) (x))
 
-#define virt_to_pfn(kaddr)	(__pa(kaddr) >> PAGE_SHIFT)
-#define pfn_to_virt(pfn)	__va((pfn) << PAGE_SHIFT)
+static inline unsigned long virt_to_pfn(const void *kaddr)
+{
+	return __pa(kaddr) >> PAGE_SHIFT;
+}
+#define virt_to_pfn virt_to_pfn
+static inline void *pfn_to_virt(unsigned long pfn)
+{
+	return __va(pfn) << PAGE_SHIFT;
+}
+#define pfn_to_virt pfn_to_virt
 
 #define virt_to_page(addr)	pfn_to_page(virt_to_pfn(addr))
 #define page_to_virt(page)	pfn_to_virt(page_to_pfn(page))