fixed at91sam9260 context thread issue, avoid idle thread stack overflow
enable at91sam9260 mmu, update SDIO and EMAC drivers
fixed context thread issue when using armcc compile
clean up code
add At91SAM9260 SDIO highspeed and SDIO IRQ capability, fixed compiling warnning
Merge pull request #77 from weety/at91sam9260

Fixed At91sam9260 context switch issue, enable mmu, update SDIO and EMAC drivers