Partially reverted 08f1bbe0c7.
The host should have this flexibility, which is consistent to the cs_hold argument.
However, the user should know as less as possible about the host.
So the wrapper layer (esp_flash_spi_init.c) should cover this, helping to set cs_setup to 1, to meet the common requirements.
DIO works with the same connections as Fast Read, so use it by
default. Also correct the note in README.md which says that DIO
requires additional pins.