x86/crc32: improve crc32c_arch() code generation with clang

x86/crc32: improve crc32c_arch() code generation with clang

crc32c_arch() is affected by
https://github.com/llvm/llvm-project/issues/20571 where clang
unnecessarily spills the inputs to "rm"-constrained operands to the
stack.  Replace "rm" with ASM_INPUT_RM which partially works around this
by expanding to "r" when the compiler is clang.  This results in better
code generation with clang, though still not optimal.

Link: https://lore.kernel.org/r/20250210210741.471725-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>