- call rtc_gpio_init for pins which aren't configured as RTC by default
- for RTC IOs 16 and 17, read higher part of the input register
- automatically convert GPIO number into RTC IO number
- use ulp_set_wakeup_period instead of writing to register
To increase the chances that the examples work out of the box, this
change is raising the default deep sleep wakeup delay to 1ms.
If GPIO15 is low at startup, ROM code takes less time to execute
(because no logging is performed), so more time may be needed to allow
flash chip to become ready.
