platform/mulle: Flash use spi driver.

 - Uses new SPI driver in cpu/arm/k60
 - Remove unnecessary disabling of interrupts in xmem.

Flash memory access is already protected inside flash.c by
spi_acquire_bus/spi_release_bus.

Interrupts must not be disabled when calling spi_transfer_blocking
since that will wait for an IRQ driven transfer to finish.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Use spi driver for lis3dh.

LIS3DH is now using SPI driver in cpu/arm/k60.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>