Implement sleep function for external flash

[YutingYou]

Feature

Implement sleep function for external flash

Steps to Test

Test the sleep API with the example application, make sure the sleep API won't affect the behavior of the file system.

Example App

void setup(void) {
}

void loop() {
    static int index = 0;
    EEPROM.begin();
    EEPROM.write(10, '0' + index++ % 10);
    Log.info("Read: %c", EEPROM.read(10));
    EEPROM.end();
    hal_exflash_sleep(true, nullptr);
    delay(1000);
    hal_exflash_sleep(false, nullptr);
}

References

[CH55886]

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[avtolstoy]

Just one minor thing: after this command you might need to send QSPI_STD_CMD_WRSR. Double check the datasheet.