ad_serdes_in: General update

Added a parameter for option SDR / DDR mode, added a parameter for parallel data width.
Note: default IF_TYPE is SDR and default PARALLEL_WIDTH is 8
axi_ad9434: Deleted unused ip file

ad_lvds_in.v is not used in this ip core.
ad9434_fmc: Fix SPI interface
ad9434_fmc: Fix PN monitor.

No need to flop the incoming data.
ad9434_fmc: Fix pin constraints for ZC706
axi_ad9434: Independent read/write update

Independent read/write is supported on "up" interface.
ad9434_fmc: Fix adc_valid signal path