This commit provides an interface to register ISRs that run from
IRAM and keeps track of the non-IRAM interrupts. It enables, for
instance, to avoid disabling all the interrupts during a SPI flash
operation: IRAM-enabled ISRs are, then, able to run during these
operations.
It also makes the code look more similar to the ESP32-S3 SPI flash
implementation by creating a common `esp32_spiflash_init` that is
responsible to create the SPI flash operation tasks. The function
intended to initialize the SPI flash partions was, then, renamed to
`board_spiflash_init`.
