Defines starting with `e' in src/dsp

• ENABLE_DSP_EMU src/dsp/dsp.h:26
• EXT_P_MEMORY src/dsp/dsp_cpu.c:110
• EXT_X_MEMORY src/dsp/dsp_cpu.c:108
• EXT_Y_MEMORY src/dsp/dsp_cpu.c:109