feat: make kernel architecture-agnostic; primitive work on arm port

kernel/linker-aarch64.ld

@@ -22,6 +22,7 @@ SECTIONS
     /* Any address in this region will do, but often 0xffffffff80000000 is chosen as */
     /* that is the beginning of the region. */
     . = 0xffffffff80000000;
+    KernelStartSymbol = .;
 
     /* Define a section to contain the Limine requests and assign it to its own PHDR */
     .limine_requests : {
@@ -74,4 +75,6 @@ SECTIONS
         *(.eh_frame*)
         *(.note .note.*)
     }
+
+    KernelEndSymbol = .;
 }