kasli/spi_flash: investigate and implement quad i/o read

[jordens]

979e363

Datasheet

Only reads 0xcc (IO2/IO3 pulled high, IO0/IO1 pulled low). Looks like the flash doesn't understand the command. And I made sure the mode bits during the dummy cycles are set correctly.
Low priority as dual i/o read works fine and this is not speed critical.

0x700cb820  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................                
0x700cb830  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
0x700cb840  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................              
0x700cb850  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
0x700cb860  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................                                                             
0x700cb870  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
0x700cb880  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................                    
0x700cb890  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
0x700cb8a0  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
0x700cb8b0  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
0x700cb8c0  cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................