sw:vec: Add scalar build support to build rv32im binaries

Add CMake option "BUILD_SIMPLIFIED_CORE" to use the macros defined in
https://spacebeaker-review.googlesource.com/c/shodan/sw/vec/+/18021
to build rv32im SW binaries.

Also remove the unused "riscv_vector.h" header file in the softrvv test
code. The header checks the vector extension in the compilation -march
flag and fails if v-ext is not used. Instead of guard it with the macro,
I remove the unused header.

Change-Id: I85c81cf2d63c232dac53ae15826753d3dd117aa8
27 files changed