SPI1 clock division control register.
| CLKCNT_L | In the master mode it must be equal to spi_mem_clkcnt_N. |
| CLKCNT_H | In the master mode it must be floor((spi_mem_clkcnt_N+1)/2-1). |
| CLKCNT_N | In the master mode it is the divider of spi_mem_clk. So spi_mem_clk frequency is system/(spi_mem_clkcnt_N+1) |
| CLK_EQU_SYSCLK | reserved |