drivers: flash_mspi_nor: Complete handling of QER, add handling of OER

Complete implementation of quad_enable_set() by adding support for all
possible Quad Enable Requirements (QER) as specified by the SFDP JEDEC
standard (JESD216). Add also corresponding octal_enable_set() to handle
Octal Enable Requirements.

Also remove initial waiting from mxicy_mx25r_post_switch_mode() which
became unneeded, as now such waiting is done in cmd_wrsr() which is
called at the end of quad_enable_set().

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>