[MinnowBoard] PCI Express config for 4x mode

[Grigory V. Korotov]

Hi,
I build my own board based on MBMax
Could someone tell me how i can configure PCI express for x4 mode?
I look into E3800 datasheet(chapter 23.2.1) and found that default 
config is 4 x1 and it is possible to change mode via SoftStrap bits 
stored in SPI flash.
Where i can learn about SoftStrap bits format and how i can change this 
bits?

Thanks.