riscv: vmlinux.lds.S: explicitly catch .init.bss sections from EFI stub

When enabling linker orphan section warning, I got warnings similar as
below:
ld.lld: warning:
./drivers/firmware/efi/libstub/lib.a(efi-stub-helper.stub.o):(.init.bss)
is being placed in '.init.bss'

Catch the sections so that we can enable linker orphan section warning.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20230119155417.2600-5-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/vmlinux.lds.S

@@ -87,6 +87,9 @@ SECTIONS
 	/* Start of init data section */
 	__init_data_begin = .;
 	INIT_DATA_SECTION(16)
+	.init.bss : {
+		*(.init.bss)	/* from the EFI stub */
+	}
 	.exit.data :
 	{
 		EXIT_DATA