Select device for FPGA specific attributes since `intelfpga` namespace was deprecated in favor of just intel namespace

[smanna12]

Previously we had FPGA specific attributes in intelfpga namespace, so it was pretty much obvious to which device they belong. Now when intelfpga was deprecated in favor of just intel namespace we can re-consider texts in some warnings etc, but it can be done in a separate patch.

Originally posted by @MrSidims in #2734 (comment)

[smanna12]

@MrSidims Could you please elaborate what do you mean to say here? We already have deprecated warning for [[intelfpga::...]] spelling. I could not locate the source codes where we are selecting the device for FPGA specific attributes.

[MrSidims]

@smanna12 my comment was an answer to this one: #2734 (comment)

[MrSidims]

So, what I mean is: FPGA hardware is kinda different from CPU and many developers are unfamiliar with it (for example Mary aknowledge that). Previously these attributes were placed in intelfpga:: namespace, so it was obvious to which device they serve. Now, when we depreceted intelfpga:: namespace in favor of intel:: namespace (which doesn't explicitly state for what device a particular attribute is implemented), it would be good to go through docs/warnings and add a note about FPGA device (so texts that describes some H/W specific logic wouldn't be looking like some wierd magic :) ).