soc: xtensa: rework DT_L2_SRAM and DT_L2_SRAM

Rename DT_L2_SRAM_* to just L2_SRAM_* and set it using new DT macros.
Do something similar for DT_LP_SRAM_* renamed to LP_SRAM_*

Updated the intel_gna driver as it used the DT_L2_SRAM_* defines.

This change also lets us remove dts_fixup.h on intel_s1000 and
intel_apl_adsp SoCs.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>