hwrng: starfive - Add TRNG driver for StarFive SoC

This adds driver support for the hardware random number generator in
Starfive SoCs and adds StarFive TRNG entry to MAINTAINERS.

Co-developed-by: Jenny Zhang <jenny.zhang@starfivetech.com>
Signed-off-by: Jenny Zhang <jenny.zhang@starfivetech.com>
Signed-off-by: Jia Jie Ho <jiajie.ho@starfivetech.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>