esp8266: NMI not disabled when timer1 ISR cleared

[mikee47]

Fixes #2763.

SDK doesn't actually disable NMI interrupts when interrupt callback cleared. This blocks regular (FRC) timer1 interrupts if subsequently enabled.

The HardwareTimer (timer1) appears to stop working if applications switch from using NMI interrupts to regular timer interrupts.

A more subtle manifestation of this bug is that the original NMI callback continues to be called when a different FRC handler is set.

TODO:

• Check nothing else gets broken (e.g. Wifi)
• Currently using SDK 3.0.3; does anything change in 3.0.4 or 3.0.5 ?

[what-the-diff]

PR Summary

• Hardware Timer Interrupt Detachment
  A piece of code was added to the 'hw_timer1_detach_interrupt' function. This allows the system to disconnect or 'detach' a particular hardware timer's interrupt, improving the capability for managing hardware resources.

• Definition of NMI_INT_ENABLE_REG
  A new line that articulates 'NMI_INT_ENABLE_REG' was incorporated into the file named eagle_soc.h. This line helps establish a standard for non-maskable interrupts, resulting in an enhanced system interaction with these interrupts.