arm:increase the mmc driver process priority.
arm:increase the mmc driver process priority.

Increase driver process priority to prevent starvation. Without
special attribute drivers will have the same priority as other
userland processes this. Posix test 1 was taking so much resources
that it triggered alarms in the MMC driver.

Change-Id: Icd3295d8f2a4a284418327a3715641fe9a3b3043

veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi