MSPI external RAM timing calibration register
| SPI_SMEM_TIMING_CLK_ENA | For sram, the bit is used to enable timing adjust clock for all reading operations. |
| SPI_SMEM_TIMING_CALI | For sram, the bit is used to enable timing auto-calibration for all reading operations. |
| SPI_SMEM_EXTRA_DUMMY_CYCLELEN | For sram, add extra dummy spi clock cycle length for spi clock calibration. |
| SPI_SMEM_DLL_TIMING_CALI | Set this bit to enable DLL for timing calibration in DDR mode when accessed to EXT_RAM. |