fs: littlefs: sample: Add test with binary pattern file modification

This commit extends the littlefs test to use binary pattern file.

This file has the 0x55 and 0xAA patterns (to avoid fast wear leveling)
written alternately with special "marks" bytes on each eight position.
Those values are incremented each time the board boots. One can adjust
the size of this file with the TEST_FILE_SIZE define.

Signed-off-by: Lukasz Majewski <lukma@denx.de>