arch: xtensa: add macros for user registers
arch: xtensa: add macros for user registers

This patch adds RUR and WUR macros to read and write user special
registers.

Signed-off-by: Tomasz Leman <b95f6f4cb1ad956ce2cfa29368a30256aa48db3f@intel.com>

finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr