When light sleep is started, the other CPU gets halted using DPORT
stall mechanism. This can happen while it is inside an esp_timer
critical section, which may lead to a deadlock. This change adds
functions to take and release esp_timer lock before entering
DPORT critical section, preventing the deadlock.
Moves the ets_timer_arm() / ets_timer_disarm() code paths to RAM
Overhead is 740 bytes of IRAM, 0 bytes DRAM
(For comparison: If all of esp_timer.c is moved to RAM, overhead is 1068 bytes IRAM and 480 bytes DRAM.)
The implementation of esp_timer_get_time used a critical section, which
resulted in a call time of ~1.8us. To make esp_timer_get_time more
useable as a high-resolution time source, this change replaces the lock
with polling. Call time is reduced to ~0.7us.
