Merge branch 'bugfix/frc1_timer_clear' into 'master'

newlib: fix register used for DPORT/RTC bug workaround

While there was no register at DR_REG_FRC_TIMER_BASE + 0x60, due to
peripheral address space wraparound this write actually affected one of
FRC2 registers, which is used by WiFi stack to implement legacy
ets_timer APIs.
This change uses FRC_TIMER_LOAD_REG(0) instead, which can be set to
known value safely.

See merge request !449