Improved CPU frequency control.

The maximum frequency for applications was set to 430 MHz before,
while some Dingoos can handle higher frequencies. Now the limit is set to
the theoretical maximum frequency of 500 MHz.

For the menu itself the maximum frequency is set to a safer 408 MHz,
to avoid over-eager users from putting their system in an unusable state
that is difficult to recover from.

Also the frequency settings are now done in 24 MHz increments, to match
the limitations of the current JZ4740 kernel. Note that only new entries
are rounded to 24 MHz multiples, existing entries stay as they are.

src/gmenu2x.h

@@ -106,6 +106,12 @@ private:
 	unsigned short cpuX; //!< Offset for displaying cpu clock information
 	unsigned short volumeX; //!< Offset for displaying volume level
 	unsigned short manualX; //!< Offset for displaying the manual indicator in the taskbar
+	unsigned cpuFreqMin; //!< Minimum CPU frequency
+	unsigned cpuFreqMax; //!< Maximum theoretical CPU frequency
+	unsigned cpuFreqSafeMax; //!< Maximum safe CPU frequency
+	unsigned cpuFreqMenuDefault; //!< Default CPU frequency for gmenu2x
+	unsigned cpuFreqAppDefault; //!< Default CPU frequency for launched apps
+	unsigned cpuFreqMultiple; //!< All valid CPU frequencies are a multiple of this
 	/*!
 	Reads the current battery state and returns a number representing it's level of charge
 	@return A number representing battery charge. 0 means fully discharged. 5 means fully charged. 6 represents a gp2x using AC power.
@@ -156,6 +162,7 @@ private:
 
 	void tvout_on(bool pal);
 	void tvout_off();
+	void initCPULimits();
 	void init();
 	void deinit();
 	void toggleTvOut();