RISC-V: errata: Use medany for relocatable builds

RISC-V: errata: Use medany for relocatable builds

We're trying to mix non-PIC/PIE objects into the otherwise-PIE
relocatable kernels, to avoid GOT/PLT references during early boot
alternative resolution (which happens before the GOT/PLT are set up).

riscv64-unknown-linux-gnu-ld: arch/riscv/errata/sifive/errata.o: relocation R_RISCV_HI20 against `tlb_flush_all_threshold' can not be used when making a shared object; recompile with -fPIC
riscv64-unknown-linux-gnu-ld: arch/riscv/errata/thead/errata.o: relocation R_RISCV_HI20 against `riscv_cbom_block_size' can not be used when making a shared object; recompile with -fPIC

Fixes: 8dc2a7e8027f ("riscv: Fix relocatable kernels with early alternatives using -fno-pie")
Link: https://lore.kernel.org/r/20250326224506.27165-2-palmer@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>