samples: A test app for spi flash

Demonstrate the use of SPI flash driver API on Arduino 101 board.

This is a re-submit of a previous merged patch which was reverted
because merge sequence was incorrect (the test app got merged
before the driver).

Origin: Original

Change-Id: I3fce61488ed7d48f400c12448f1c7a01c555661c
Signed-off-by: Baohong Liu <baohong.liu@intel.com>