mtd: spi-nor: Add support for Infineon s25fs256t

Infineon S25FS256T is 256Mbit Quad SPI NOR flash. The key features and
differences comparing to other Spansion/Cypress flash familes are:
  - 4-byte address mode by factory default
  - Quad mode is enabled by factory default
  - Supports mixture of 128KB and 64KB sectors by OTP configuration
    (this patch supports uniform 128KB only)

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