hwrng: mtk - add mt7986 support

1. Add trng compatible name for MT7986
2. Fix mtk_rng_wait_ready() function

Signed-off-by: Mingming.Su <Mingming.Su@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>