fix(st-ddr): remove TODO in STM32MP2 driver

Remove useless ddr_get_io_calibration_val service.
Other items are deleted as they're useless on STM32MP2 series.

Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@foss.st.com>
Change-Id: I30bb18f156ff6dc06147987654363472a1e0182d
3 files changed