C20_MPLLB_TX_CLK_DIV_MASK
tx_clk_div = REG_FIELD_GET(C20_MPLLB_TX_CLK_DIV_MASK, pll_state->mpllb[0]);
#define MPLL_TX_CLK_DIV(val) REG_FIELD_PREP16(C20_MPLLB_TX_CLK_DIV_MASK, val)