mtd: spi-nor: spansion: Fixup params->set_4byte_addr_mode for SEMPER

Infineon SEMPER flash family does not support E9h opcode as Exit 4-byte
mode (EX4B). Therefore, params->set_4byte_addr_mode is not determined by
BFPT parse. Fixup it up by introducing vendor specific EX4B opcode (B8h)
and function.

Fixes: c87c9b11 ("mtd: spi-nor: spansion: Determine current address mode")
Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Acked-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://lore.kernel.org/r/20250612074427.22263-1-Takahiro.Kuwano@infineon.com