All the users in the kernel are gone and generated .config files from
previous LTS kernels will contain ARCH_SIFIVE. Drop SOC_SIFIVE and
update the defconfig.
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>