drivers: spi: spi_nrfx_spim: Add additional symbol check for frequency

Some targets may not have `NRF_SPIM_HAS_32_MHZ_FREQ` or
`NRF_SPIM_HAS_16_MHZ_FREQ` symbols but have `NRF_SPIM_HAS_PRESCALER`
symbol defined. The symbol informs that target supports 32 MHz and
16 MHz frequencies for SPIM instances.

Signed-off-by: Adam Wojasinski <adam.wojasinski@nordicsemi.no>