cpu: riscv: set correct SMBIOS processor family value

The SMBIOS specification requires to set the processor family in the type 4
(Processor Information) table to specific values depending only on the
bitness of the system (0x200 for RV32 and 0x201 for RV64).

With this patch dmidecode shows

    Handle 0x0004, DMI type 4, 48 bytes
    Processor Information
	Socket Designation: Not Specified
	Type: Central Processor
	Family: RV64

for qemu-riscv64_smode_defconfig.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>