efi: fix -Wmissing-variable-declarations warning

When building x86/defconfig with Clang-18 I encounter the following warnings:
| arch/x86/platform/efi/efi.c:934:23: warning: no previous extern declaration for non-static variable 'efi_attr_fw_vendor' [-Wmissing-variable-declarations]
|   934 | struct kobj_attribute efi_attr_fw_vendor = __ATTR_RO(fw_vendor);
| arch/x86/platform/efi/efi.c:935:23: warning: no previous extern declaration for non-static variable 'efi_attr_runtime' [-Wmissing-variable-declarations]
|   935 | struct kobj_attribute efi_attr_runtime = __ATTR_RO(runtime);
| arch/x86/platform/efi/efi.c:936:23: warning: no previous extern declaration for non-static variable 'efi_attr_config_table' [-Wmissing-variable-declarations]
|   936 | struct kobj_attribute efi_attr_config_table = __ATTR_RO(config_table);

These symbols are declared extern in drivers/firmware/efi/efi.c. Move
the declarations to linux/efi.h to resolve these warnings.

Also, trim a trailing space from efi_set_variable_t typedef.

Link: ClangBuiltLinux#1920
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>

drivers/firmware/efi/efi.c

@@ -161,9 +161,6 @@ static ssize_t fw_platform_size_show(struct kobject *kobj,
 	return sprintf(buf, "%d\n", efi_enabled(EFI_64BIT) ? 64 : 32);
 }
 
-extern __weak struct kobj_attribute efi_attr_fw_vendor;
-extern __weak struct kobj_attribute efi_attr_runtime;
-extern __weak struct kobj_attribute efi_attr_config_table;
 static struct kobj_attribute efi_attr_fw_platform_size =
 	__ATTR_RO(fw_platform_size);
 

include/linux/efi.h

@@ -287,7 +287,7 @@ typedef efi_status_t efi_get_variable_t (efi_char16_t *name, efi_guid_t *vendor,
 					 unsigned long *data_size, void *data);
 typedef efi_status_t efi_get_next_variable_t (unsigned long *name_size, efi_char16_t *name,
 					      efi_guid_t *vendor);
-typedef efi_status_t efi_set_variable_t (efi_char16_t *name, efi_guid_t *vendor, 
+typedef efi_status_t efi_set_variable_t (efi_char16_t *name, efi_guid_t *vendor,
 					 u32 attr, unsigned long data_size,
 					 void *data);
 typedef efi_status_t efi_get_next_high_mono_count_t (u32 *count);
@@ -632,6 +632,10 @@ typedef struct {
 
 extern unsigned long __ro_after_init efi_rng_seed;		/* RNG Seed table */
 
+extern __weak struct kobj_attribute efi_attr_fw_vendor;
+extern __weak struct kobj_attribute efi_attr_runtime;
+extern __weak struct kobj_attribute efi_attr_config_table;
+
 /*
  * All runtime access to EFI goes through this structure:
  */