board: st: Update LED management for stm32mp1

board: st: Update LED management for stm32mp1

Remove get_led() and setup_led() which became obsolete since
led_boot_on() introduction. led_boot_on() is automatically called
from board_r.c

Regarding "u-boot,error-led" property can't be used anymore since commit
Since commit 516a13e8db32 ("led: update LED boot/activity to new property implementation")

Instead get the LED labeled "red:status".
See kernel series: https://patchwork.kernel.org/project/linux-arm-kernel/list/?series=1022570

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>