[README][Docs] Update LLVM compiler name in README and related documentation

[dnhsieh-intel]

Description

This PR replaces the usage of "Intel project for LLVM* technology" with the approved one "oneAPI DPC++ Compiler". In addition, the tables of "Supported Configurations" in README are reorganized for better readability.

Note that the current format of the tables is "library-centric":

Domain	Backend	Library	Supported Link Type	Supported Compiler
BLAS	x86 CPU	Intel(R) oneAPI Math Kernel Library	Dynamic, Static	DPC++, LLVM*, hipSYCL
	Intel GPU		Dynamic, Static	DPC++
	...	...	...	...
	x86 CPU, Intel GPU, NVIDIA GPU, AMD GPU	portBLAS	Dynamic, Static	DPC++, LLVM*

The underlying message of this table format is what a library can support. The table at the top of README already roughly covers this aspect.

The proposed table format is "application-centric":

Domain	Backend	Library	Supported Compiler	Supported Link Type
BLAS	x86 CPU	Intel(R) oneMKL	Intel DPC++ Open DPC++ hipSYCL	Dynamic, Static
		NETLIB LAPACK	Intel DPC++ Open DPC++ hipSYCL	Dynamic, Static
		portBLAS	Intel DPC++ Open DPC++	Dynamic, Static
	Intel GPU	Intel(R) oneMKL	Intel DPC++	Dynamic, Static
		portBLAS	Intel DPC++ Open DPC++	Dynamic, Static
	...	...	...	...

For example, if an application requires BLAS on Intel GPUs, this format would make it easier to find out what configurations are available for the given application.

Checklist

All Submissions

• Do all unit tests pass locally? N/A, only documentation changes.
• Have you formatted the code using clang-format? N/A, only documentation changes.

[dnhsieh-intel]

@Rbiessy Please help checking the supported compilers for portBLAS and portFFT in the tables. I suspect that some slots might need to be changed.

[hjabird]

I think the tables look less cluttered with your changes. Thanks!

[dnhsieh-intel]

The update of the supported commit of oneAPI DPC++ Compiler and OS will be done in a separate PR.