Update to support new part numbers.

Add new STM32 MPUs Part = STM32MP151F, STM32MP153F, STM32MP157F,
STM32MP151D, STM32MP153D, STM32MP157D

The STM32MP1 series is available in 3 different lines which are pin-to-pin
compatible:
- STM32MP157: Dual Cortex-A7 cores, Cortex-M4 core @ 209 MHz,
              3D GPU, DSI display interface and CAN FD
- STM32MP153: Dual Cortex-A7 cores, Cortex-M4 core @ 209 MHz
              and CAN FD
- STM32MP151: Single Cortex-A7 core, Cortex-M4 core @ 209 MHz

Each line comes with a security option (cryptography & secure boot)
& a Cortex-A frequency option :

- A      Basic + Cortex-A7 @ 650 MHz
- C      Secure Boot + HW Crypto + Cortex-A7 @ 650 MHz
- D      Basic + Cortex-A7 @ 800 MHz
- F      Secure Boot + HW Crypto + Cortex-A7 @ 800 MHz

Remove useless variable in stm32mp_is_single_core().

Change-Id: Id30c836af986c6340c91efa8a7ae9480a2827089
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>