add: xcorr 211.875 kHz option

The FPGA supported this frequency for a long time, just the ARM code
had no define to enable it.

armsrc/fpgaloader.h

@@ -74,6 +74,7 @@ extern void switch_off(void);
 // Options for the HF reader, correlating against rx from tag
 #define FPGA_HF_READER_RX_XCORR_848_KHZ				(1<<0)
 #define FPGA_HF_READER_RX_XCORR_SNOOP				(1<<1)
+#define FPGA_HF_READER_RX_XCORR_QUARTER				(1<<2)
 // Options for the HF simulated tag, how to modulate
 #define FPGA_HF_SIMULATOR_NO_MODULATION				(0<<0) // 0000
 #define FPGA_HF_SIMULATOR_MODULATE_BPSK				(1<<0) // 0001