riscv: vmlinux.lds.S: explicitly catch .riscv.attributes sections

When enabling linker orphan section warning, I got warnings similar as
below:
riscv64-linux-gnu-ld: warning: orphan section `.riscv.attributes' from
`init/main.o' being placed in section `.riscv.attributes'

While I don't see any usage of .riscv.attributes sections' in kernel
now, just 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/20230119155417.2600-4-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/vmlinux.lds.S

@@ -146,6 +146,7 @@ SECTIONS
 	STABS_DEBUG
 	DWARF_DEBUG
 	ELF_DETAILS
+	.riscv.attributes 0 : { *(.riscv.attributes) }
 
 	DISCARDS
 }