Add simulation commands to example/picosoc

[kanade-k-1228]

Hi,

I've added simulation to this sample code. The major changes I made are as follows:

1. Added simulation command to Makefile.
2. Added a simple shell script for padding the binary written to SPI Flash.
   • Is there an option of tinyprog available to output the binary written to the SPI flash as a file?
3. Added a define in C to use single IO mode during simulation.
   • Because the spiflash module does not support dual IO mode.