logging: simplify is_rodata() for NIOS2, RISC-V and SPARC
logging: simplify is_rodata() for NIOS2, RISC-V and SPARC

NIOS2, RISC-V and SPARC are using _image_rodata_start/_end in
their linker scripts to mark the boundaries of rodata. So
they no loner need special treatment.

Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

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