arm64: dts: st: Add memory-region-names property for stm32mp257f-ev1

arm64: dts: st: Add memory-region-names property for stm32mp257f-ev1

In order to set the AMCR register, which configures the
memory-region split between ospi1 and ospi2, we need to
identify the ospi instance.

By using memory-region-names, it allows to identify the
ospi instance this memory-region belongs to.

Fixes: cad2492de91c ("arm64: dts: st: Add SPI NOR flash support on stm32mp257f-ev1 board")
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20251031-upstream_fix_dts_omm-v4-1-e4a059a50074@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>