drivers: spi_nrfx_spim: Incorrect handling of extended SPIM configuration

[anangl]

Describe the bug
Extended SPIM configuration (needed by the SPI_3_NRF_RX_DELAY Kconfig option) is not handled correctly in spi_nrfx_spim.c. In result, no other SPIM instance can be enabled together with SPIM3.

To Reproduce

1. In the hello_world sample, add the following lines to prj.conf:

CONFIG_SPI=y
CONFIG_SPI_2=y
CONFIG_SPI_2_NRF_SPIM=y
CONFIG_SPI_3=y

and create a file named nrf52840_pca10056.overlay with the following content:

&spi2 {
	compatible = "nordic,nrf-spim";
};

2. Try to build the sample for the nrf52840_pca10056 board:

west build -b nrf52840_pca10056

3. See that compilation fails.

Expected behavior
Successful build.

Impact
showstopper

Screenshots or console output

spi_nrfx_spim.c:365:14: error: 'CONFIG_SPI_2_NRF_RX_DELAY' undeclared here (not in a function); did you mean 'CONFIG_SPI_3_NRF_RX_DELAY'?
  .rx_delay = CONFIG_SPI_##idx##_NRF_RX_DELAY,
              ^~~~~~~~~~~

Environment (please complete the following information):

• OS: Linux
• Toolchain: Zephyr SDK
• Zephyr 2.1.0 rc2 (92e017f) but the same error will occur for Zephyr 1.14.1 (77c455c)