sysreset: diverge GPIO reset and poweroff configs per-phase

sysreset: diverge GPIO reset and poweroff configs per-phase

GPIO reset and power-off functionality depends on device tree data, which
is often absent in SPL or TPL. To address this, incorporate PHASE_ into the
config option and add Kconfig option or each phase.

Adjust SYSRESET_GPIO and POWEROFF_GPIO uses to address possible
regressions.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>