arm: dts: stm32mp1: Drop fastboot and stm32prog trigger gpios on DHCOM

PA13 and PA14 are used for USB power control and can't be used
to enforce fastboot or stm32prog mode by pressing a button.

Defining CONFIG_FASTBOOT/CONFIG_CMD_STM32PROG without this patch applied
results in fastboot/stm32prog always starting, because PA13/PA14 are always
low during boot. So drop the wrong trigger gpios definitions.

Signed-off-by: Johann Neuhauser <jneuhauser@dh-electronics.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>