string-table: Introduce DECLARE_STRING_TABLE_LOOKUP() and friends

Let's introduce these for the following two reasons:
- Using them makes sure the parameter names match between declaration
  and definition (if both use the corresponding macros).
- They make sure developers can't forget the _const_ and _pure_
  attributes for the declarations.

This commit also includes some include sorting fixes

src/boot/efi-log.h

@@ -34,8 +34,7 @@ typedef enum LogLevel {
         _LOG_INVALID = -1,
 } LogLevel;
 
-LogLevel log_level_from_string(const char *s) _pure_;
-const char* log_level_to_string(LogLevel l) _const_;
+DECLARE_STRING_TABLE_LOOKUP(log_level, LogLevel);
 
 LogLevel log_get_max_level(void) _pure_;
 int log_set_max_level(LogLevel level);

src/boot/efi.h

@@ -13,6 +13,7 @@
 #include "cleanup-fundamental.h"        /* IWYU pragma: export */
 #include "efi-fundamental.h"            /* IWYU pragma: export */
 #include "macro-fundamental.h"          /* IWYU pragma: export */
+#include "string-table-fundamental.h"   /* IWYU pragma: export */
 
 #if SD_BOOT
 /* uchar.h/wchar.h are not suitable for freestanding environments. */

src/boot/secure-boot.h

@@ -41,5 +41,5 @@ void install_security_override(security_validator_t validator, const void *valid
 void uninstall_security_override(void);
 bool security_override_available(void);
 
-const char* secure_boot_enroll_to_string(secure_boot_enroll e) _const_;
-const char* secure_boot_enroll_action_to_string(secure_boot_enroll_action e) _const_;
+DECLARE_STRING_TABLE_LOOKUP_TO_STRING(secure_boot_enroll, secure_boot_enroll);
+DECLARE_STRING_TABLE_LOOKUP_TO_STRING(secure_boot_enroll_action, secure_boot_enroll_action);