spi_flash: protect esp_intr_noniram_{disable,enable} in 1-core config

spi_flash: protect esp_intr_noniram_{disable,enable} in 1-core config

MR !441 (7c155ab) has fixed issue with esp_intr_noniram_{disable,enable}
calls not being properly protected by spi_flash_op_{lock,unlock}.
Unit test was added, but the unit test environment tests only dual-core
config. Similar issue was present in the code path for the single-core
config, where esp_intr_noniram_{disable,enable} calls were unprotected.

This change fixes the protection issue and updates the unit test to
run properly in single core config as well.

The issue with running unit tests for single core config will be
addressed in a separate MR.