aarch64: filter $x from kallsyms

Similar to ARM, AArch64 is generating $x and $d syms... which isn't
terribly helpful when looking at %pF output and the like. Filter those
out in kallsyms, modpost and when looking at module symbols.

Seems simplest since none of these check EM_ARM anyway, to just add it
to the strchr used, rather than trying to make things overly
complicated.

initcall_debug improves:
dmesg_before.txt: initcall $x+0x0/0x154 [sg] returned 0 after 26331 usecs
dmesg_after.txt: initcall init_sg+0x0/0x154 [sg] returned 0 after 15461 usecs

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

scripts/mod/modpost.c

@@ -1146,7 +1146,7 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf64_Sword addr,
 
 static inline int is_arm_mapping_symbol(const char *str)
 {
-	return str[0] == '$' && strchr("atd", str[1])
+	return str[0] == '$' && strchr("axtd", str[1])
 	       && (str[2] == '\0' || str[2] == '.');
 }