ARM: dts: stm32: stm32mp151a-prtt1l: Fix QSPI configuration

ARM: dts: stm32: stm32mp151a-prtt1l: Fix QSPI configuration

Rename 'pins1' to 'pins' in the qspi_bk1_pins_a node to correct the
subnode name. The incorrect name caused the configuration to be
applied to the wrong subnode, resulting in QSPI not working properly.

Some additional changes was made:
- To avoid this kind of regression, all references to pin configuration
  nodes are now referenced directly using the format &{label/subnode}.
- /delete-property/ bias-disable; was added everywhere where bias-pull-up
  is used
- redundant properties like driver-push-pull are removed

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>