1bitsquared_icebreaker: Add test code to use LiteSPI.
1bitsquared_icebreaker: Add test code to use LiteSPI.

Both XiP from SPI(1X) or QSPI(4X) are working, but resource usage is currently
too high to be able to switch to it by default. We'll first try to reduce it.

Resource usage using SPI(1X) and actual LiteX SPI Flash core:
Info: Device utilisation:
Info: 	         ICESTORM_LC:  2016/ 5280    38%
Info: 	        ICESTORM_RAM:     2/   30     6%
Info: 	               SB_IO:    15/   96    15%
Info: 	               SB_GB:     8/    8   100%
Info: 	        ICESTORM_PLL:     1/    1   100%
Info: 	         SB_WARMBOOT:     0/    1     0%
Info: 	        ICESTORM_DSP:     0/    8     0%
Info: 	      ICESTORM_HFOSC:     0/    1     0%
Info: 	      ICESTORM_LFOSC:     0/    1     0%
Info: 	              SB_I2C:     0/    2     0%
Info: 	              SB_SPI:     0/    2     0%
Info: 	              IO_I3C:     0/    2     0%
Info: 	         SB_LEDDA_IP:     0/    1     0%
Info: 	         SB_RGBA_DRV:     0/    1     0%
Info: 	      ICESTORM_SPRAM:     4/    4   100%


Resource usage using LiteSPI:
Info: Device utilisation:
Info: 	         ICESTORM_LC:  3964/ 5280    75%
Info: 	        ICESTORM_RAM:     2/   30     6%
Info: 	               SB_IO:    15/   96    15%
Info: 	               SB_GB:     8/    8   100%
Info: 	        ICESTORM_PLL:     1/    1   100%
Info: 	         SB_WARMBOOT:     0/    1     0%
Info: 	        ICESTORM_DSP:     0/    8     0%
Info: 	      ICESTORM_HFOSC:     0/    1     0%
Info: 	      ICESTORM_LFOSC:     0/    1     0%
Info: 	              SB_I2C:     0/    2     0%
Info: 	              SB_SPI:     0/    2     0%
Info: 	              IO_I3C:     0/    2     0%
Info: 	         SB_LEDDA_IP:     0/    1     0%
Info: 	         SB_RGBA_DRV:     0/    1     0%
Info: 	      ICESTORM_SPRAM:     4/    4   100%

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