RISC-V: Enable PMEM drivers

We now have PMEM arch support available in RISC-V kernel so let us
enable relevant drivers in defconfig.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221114090536.1662624-4-apatel@ventanamicro.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>