Switch GPIO to RTC GPIO

[tbec]

Only certain pins can be latched during light/deep sleep. For example we would like to latch the PM sensor SET/RESET lines low while sleeping, but can't do it currently. Valid GPIO numbers are:
0, 2, 4, 12, 13, 14, 15, 25, 26, 27, 32, 33, 34, 35, 36, 37, 38, 39
An easy immediate change is pin 10 is open. I forget what it's GPIO number is, but it's in this list. We could route PM_RESET here. Other changed would be more difficult and would have be discussed in more detail.

[tbec]

GPIOs during boot process:

0 - Pulled HIGH then driven low. Do not alter this pin during boot!
1 - Pulled HIGH then driven low. Do not alter this pin during boot!
2 - Pulled HIGH then driven low. Do not alter this pin during boot!
3 - Pulled HIGH. No influence on boot process
4 - High Impedance
5 - High Impedance
12 - Pulled HIGH. No influence on boot process
13 - Pulled HIGH. No influence on boot process
14 - Pulled HIGH. No influence on boot process
15 - Pulled HIGH then driven low. Do not alter this pin during boot!
16 - Driven HIGH. Do not short

https://www.esp8266.com/viewtopic.php?f=32&t=16141

We should use GPIO4 to control SET pin on the PMS, because it is high impedance during boot (and presumably during flash, which is important if we use the PMS port to flash) and will be tied together with the UART0 RX pin. This all needs to be double-checked before implementing!