RISCV: kexec: Fix build error without CONFIG_MODULES

When CONFIG_MODULES is not set/enabled:

../arch/riscv/kernel/elf_kexec.c:353:9: error: unknown type name 'Elf_Rela'; did you mean 'Elf64_Rela'?
  353 |         Elf_Rela *relas;
      |         ^~~~~~~~
      |         Elf64_Rela

Replace Elf_Rela by Elf64_Rela to avoid relying on CONFIG_MODULES.
Signed-off-by: Li Zhengyu <lizhengyu3@huawei.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20220601063924.13037-1-lizhengyu3@huawei.com
Fixes: 838b3e28 ("RISC-V: Load purgatory in kexec_file")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/elf_kexec.c

@@ -349,7 +349,7 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
 {
 	const char *strtab, *name, *shstrtab;
 	const Elf_Shdr *sechdrs;
-	Elf_Rela *relas;
+	Elf64_Rela *relas;
 	int i, r_type;
 
 	/* String & section header string table */