ARM: dts: stm32mp1: remove file stm32mp157-pinctrl.dtsi

Remove the unnecessary file stm32mp157-pinctrl.dtsi and
solve all issues introduced by the commit 89148318 ("Merge branch
 'next'") after a conflict on the patch applied in the next branch in
commit 1a4f57c8 ("ARM: dts: stm32mp1: DT alignment with Linux 5.6-rc1")

Need to reapplied on stm32mp15-pinctrl.dtsi the the 3 patches
applied previously on file "stm32mp157-pinctrl.dtsi" in v2020.04
- commit 4fdbe648 ("ARM: dts: stm32: Add alternate pinmux for SDMMC1
 direction pins")'
- commit 5fdcba64 ("ARM: dts: stm32: Add alternate pinmux for SDMMC2
 pins 4-7")'
- commit 955de511 ("ARM: dts: stm32: Add alternate pinmux for ethernet
 RGMII")'

Cc: Marek Vasut <marex@denx.de>

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>