serial/uart_ns16550: make UART_REG_ADDR_INTERVAL
serial/uart_ns16550: make UART_REG_ADDR_INTERVAL

On behalf of : Timo Teräs <timo.teras@iki.fi>

UART_REG_ADDR_INTERVAL is SOC / chip implementation specific feature,
and its width does not always correspond to current settings for
IOPORT/non IOPORT access method.

Signed-off-by: Francisco Munoz <bb61d9940d70121d393324718c73fb8bcc0ce7a0@intel.com>

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