ARM: dts: stm32: add a new DCMI pins group on stm32mp15

The Seeed Odyssey-STM32MP157C board has a 20-pin DVP camera output.
stm32mp15-pinctrl.dtsi contained one pin state definition for the DCMI
interface, dcmi-0, AKA phandle dcmi_pins_a. This definition was
incompatible with the pins used on the Odyssey board, where:
- there are 8 data pins instead of 12,
- DCMI_HSYNC is available at PA4 instead of PH8,
- DCMI_D0 is at PC6 instead of PH9,
- DCMI_D3 is at PE1 instead of PH12,
- DCMI_D4 is at PE11 instead of PH14,
- DCMI_D5 is at PD3 instead of PI4,
- DCMI_D6 is at PE13 instead of PB8,
- DCMI_D7 is at PB9 instead of PE6.

Add the DCMI pins used on the Odyssey board as a new DCMI pin state
definition, dcmi-1, AKA phandle dcmi_pins_b.

Signed-off-by: Grzegorz Szymaszek <gszymaszek@short.pl>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>