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

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

s28hx_t_setup() only checks sector layout setting. To support multi-die
package parts like S28HS02GT, it needs to check device size and assign
ready() hook for multi-die package parts. These are covered in s25_setup()
so we can consolidate s28hx_t_setup() and s25_setup() into one named
s25_s28_setup().

spi_nor_wait_till_ready() at the beginning of s28hx_t_setup() can be
removed since there is no op that makes device busy state before setup.

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