Move remaining inline assembly test files into asm directory

[taiki-e]

Before:

tests/assembly/asm/*
tests/assembly/asm-comments.rs
tests/codegen/asm-target-clobbers.rs
tests/codegen/asm-goto.rs
tests/codegen/asm-maybe-uninit.rs
tests/codegen/asm-msp430-clobbers.rs
tests/codegen/asm-options.rs
tests/codegen/asm-clobbers.rs
tests/codegen/asm-may_unwind.rs
tests/codegen/asm-arm64ec-clobbers.rs
tests/codegen/asm-powerpc-clobbers.rs
tests/codegen/asm-sanitize-llvm.rs
tests/codegen/asm-s390x-clobbers.rs
tests/codegen/asm-clobber_abi.rs
tests/codegen/asm-multiple-options.rs
tests/codegen/global_asm.rs
tests/codegen/global_asm_include.rs
tests/codegen/global_asm_x2.rs
tests/ui/asm/*

After:

tests/assembly/asm/*
tests/codegen/asm/*
tests/ui/asm/*

I moved the remaining standalone test files into the asm directory, and then either removed the "asm-" suffix or for x86-specific registers tests replaced the "asm-" suffix with the "x86-" suffix.

(Then I noticed that there is no test for clobber_abi for already stabilized aarch64, arm, riscv, and loongarch64 asm... I don't believe there is a problem like #131332, but I plan to add tests for them later.)

r? @Amanieu

@rustbot label +A-inline-assembly