Category 3:
In Option Bytes: (0x1FFF7800)
Bit 22 DBANK:
0: Single bank mode with 128 bits data read width
1: Dual bank mode with 64 bits data
This bit can be written only when PCROP1/2 is disabled.
Bit 21 Reserved, must be kept at reset value.
Bit 20 BFB2: Dual-bank boot
0: Dual-bank boot disable
1: Dual-bank boot enable
But in register : FLASH_OPTR (0x40022020)
Bits: 22:20 Reserved, must be kept cleared
