IO seek offset can be set to values above UINT32_MAX, this change
changes the seek offset argument from 'ssize_t' to 'signed long long'.
Fixing platform seek functions to match the new interface update.

Change-Id: I25de83b3b7abe5f52a7b0fee36f71e60cac9cfcb
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>