efi: Move efifb_setup_from_dmi() prototype from arch headers

Commit 8633ef8 ("drivers/firmware: consolidate EFI framebuffer setup
for all arches") made the Generic System Framebuffers (sysfb) driver able
to be built on non-x86 architectures.

But it left the efifb_setup_from_dmi() function prototype declaration in
the architecture specific headers. This could lead to the following
compiler warning as reported by the kernel test robot:

   drivers/firmware/efi/sysfb_efi.c:70:6: warning: no previous prototype for function 'efifb_setup_from_dmi' [-Wmissing-prototypes]
   void efifb_setup_from_dmi(struct screen_info *si, const char *opt)
        ^
   drivers/firmware/efi/sysfb_efi.c:70:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void efifb_setup_from_dmi(struct screen_info *si, const char *opt)

Fixes: 8633ef8 ("drivers/firmware: consolidate EFI framebuffer setup for all arches")
Reported-by: kernel test robot <lkp@intel.com>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20211126001333.555514-1-javierm@redhat.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/arm/include/asm/efi.h

@@ -17,7 +17,6 @@
 
 #ifdef CONFIG_EFI
 void efi_init(void);
-extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
 
 int efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md);
 int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);

arch/arm64/include/asm/efi.h

@@ -14,7 +14,6 @@
 
 #ifdef CONFIG_EFI
 extern void efi_init(void);
-extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
 #else
 #define efi_init()
 #endif

arch/riscv/include/asm/efi.h

@@ -13,7 +13,6 @@
 
 #ifdef CONFIG_EFI
 extern void efi_init(void);
-extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
 #else
 #define efi_init()
 #endif

arch/x86/include/asm/efi.h

@@ -197,8 +197,6 @@ static inline bool efi_runtime_supported(void)
 
 extern void parse_efi_setup(u64 phys_addr, u32 data_len);
 
-extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
-
 extern void efi_thunk_runtime_setup(void);
 efi_status_t efi_set_virtual_address_map(unsigned long memory_map_size,
 					 unsigned long descriptor_size,

include/linux/efi.h

@@ -1283,4 +1283,10 @@ static inline struct efi_mokvar_table_entry *efi_mokvar_entry_find(
 }
 #endif
 
+#ifdef CONFIG_SYSFB
+extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);
+#else
+static inline void efifb_setup_from_dmi(struct screen_info *si, const char *opt) { }
+#endif
+
 #endif /* _LINUX_EFI_H */