mtd: spi-nor-core: Consolidate post_bfpt_fixup() for Infineon(Cypress) S25 and S28

s28hx_t_post_bfpt_fixup() fixes erase opcode, erase size, and page size.
s25_post_bfpt_fixup() is doing same thing including multi-die support.
We can consolidate s28hx_t_post_bfpt_fixup() and s25_post_bfpt_fixup()
into one named s25_s28_post_bfpt_fixup().

In s25_s28_post_bfpt_fixup(), set_4byte() is called to force the device to
be 4-byte addressing mode. In S28HS02GT datasheet, the B7 opcode is missing
but it works actually (confirmed).

Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>