tests: spi_loopback: Add rv32m1 configuration

Adds a board-specific configuration for the rv32m1 VEGAboard to the
spi_loopback test.

Enabled slave number 2, and turned on debug configurations to debug
effectively and from excess code being optimized out.

Signed-off-by: Jose Manuel Pacheco Luna <manuel.pacheco@nxp.com>