SPI Host structs missing definitions for Flash and Host 2

[llorenc-m]

The only definitions in "spi_host_structs.h" are currently:

#define spi_host_peri ((volatile spi_host *) SPI_HOST_START_ADDRESS)

It should be changed to something like (since all three peripherals are the same and therefore use the same HAL):

#define spi_host1_peri ((volatile spi_host *) SPI_HOST_START_ADDRESS)
#define spi_host2_peri ((volatile spi_host *) SPI2_START_ADDRESS)
#define spi_flash_peri ((volatile spi_host *) SPI_FLASH_START_ADDRESS)