riscv/purgatory: Omit use of bin2c

The .incbin assembler directive is much faster than bin2c + $(CC).

Do similar refactoring as in commit 4c0f032d49 ("s390/purgatory:
Omit use of bin2c").

Please note the .quad directive matches to size_t in C (both 8 byte)
because the purgatory is compiled only for the 64-bit kernel.
(KEXEC_FILE depends on 64BIT).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20220625223438.835408-2-masahiroy@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

scripts/remove-stale-files

@@ -40,6 +40,8 @@ if [ -n "${building_out_of_srctree}" ]; then
 	done
 fi
 
+rm -f arch/riscv/purgatory/kexec-purgatory.c
+
 rm -f scripts/extract-cert
 
 rm -f arch/x86/purgatory/kexec-purgatory.c