drivers/ddr/fsl: Cleanup unused variable

Variable "row_density" is no longer used. Drop it from DIMM structure.

Signed-off-by: York Sun <york.sun@nxp.com>

include/fsl_ddr_dimm_params.h

@@ -40,7 +40,6 @@ typedef struct dimm_params_s {
 	unsigned int n_banks_per_sdram_device;
 #endif
 	unsigned int burst_lengths_bitmask;	/* BL=4 bit 2, BL=8 = bit 3 */
-	unsigned int row_density;
 
 	/* used in computing base address of DIMMs */
 	unsigned long long base_address;