boards: x86: arduino_101: set DISK_FLASH_MAX_RW_SIZE to 256
boards: x86: arduino_101: set DISK_FLASH_MAX_RW_SIZE to 256

set DISK_FLASH_MAX_RW_SIZE to 256, as maximum bytes that can be
programed to SPI FLASH by Page Program Command is 256.

Fixes #8506

Signed-off-by: Savinay Dharmappa <b9bdbfc60b49ae384b99e3313b3f20d055baeacb@intel.com>

Vudentz/zephyr,ldts/zephyr,nashif/zephyr,finikorg/zephyr,kraj/zephyr,explora26/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,finikorg/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,explora26/zephyr,punitvara/zephyr,ldts/zephyr,nashif/zephyr,galak/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,kraj/zephyr,explora26/zephyr,kraj/zephyr,explora26/zephyr,explora26/zephyr,kraj/zephyr,punitvara/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr