drivers: STM32H7: ethernet: PTP clock doesn’t works

fix to the HAL_API_V2 to get PTP to work

In the HAL_ETH_ReadData function where it checks for the
last descriptor, I added a checked if the TSA bit was set
in DESC1
If the TSA bit is set then have a peak at the context
descriptor which should be the one after the last
descriptor
If the CTXT bit is set in the context descriptor then
extract the timestamps

update README to fix to the V2 HAL API to get PTP to work

Co-authored-by: Chamira Perera <chamira.perera@audinate.com>
Signed-off-by: Marc Desvaux <marc.desvaux-ext@st.com>