-fsycl-targets Has misleading target triples

[hdelan]

-fsycl-targets as described in https://intel.github.io/llvm-docs/UsersManual.html has misleading target triples.

For example:

• spir64 does not generate SPIR, but rather SPIR-V.
• spir64_x86_64 does not generate SPIR or SPIR-V, but rather device code for x86_64 processors.
• spir64_gen sounds like it generates generic SPIR. It actually generates device code for Intel Graphics.

Proposals:

• Replace spir64 with spirv64
• Replace spir64_x86_64 with x86_64 or perhaps aot_x86_64
• Replace spir64_fpga with fpga or perhaps aot_fpga
• Replace spir64_gen with intel_graphics/aot_intel_graphics or something similar.