Fix mock store issues

Fixing multiple mock store issues in order to pass all PSA ITS API host
tests.
* Deny calls with 0 uid
* Handle WRITE_ONCE flags
* Handle data_offset argument in get calls

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: I63b1812482bf9e98a0ca69fc5d14757346efafae
1 file changed