Commit 64704886b7 (refactor(driver_spi): remove some SPI_LL_xxx SOC_xxx macros)
removed #include "soc/spi_periph.h" from hal/spi_hal.h. Out-of-tree code that
included hal/spi_hal.h and used spi_periph_signal then failed with the symbol
undeclared, because that header had been the transitive source of the declaration.
Partially reverts it.