splitted the terminationcontrol lines from the record types 't_tech_ddr_phy_in' and 't_tech_ddr_phy_ou'

Added g_sim_flash_model to ensure only one instance of flash model, to avoid double driver failure in sim.

Renamed key hdl_lib_uses into hdl_lib_uses_synth and added new key hdl_lib_uses_sim for extra test_bench_files library dependencies.

to quartus compile

Use g_rd_fifo_af_margin to fit one (DDR3 IP) or more (DDR4 IP) rd burst accesses of g_tech_ddr.maxburstsize each.

Improved check on snk_diag_res by placing it after the read FIFO has been read empty. No need for using v_diag_first_rd to ensure that snk_diag_res_val has become 1.

Improved stimuli using generics and functions to define the write and read block accesses. Distinghuis between tests for DDR3 and DDR4, because DDR4 model simulates about 20x slower.