[Codegen][LLVMCPU] Split loadProcessorData: hoist only the alloca (#24786)

35b2070 (#24749) fixed unbounded stack growth by moving the whole
loadProcessorData CPU-feature patch buffer construction to the function
entry block. But that also hoisted the feature-bit or/store away from
the ukernel call, and once the ukernel inlines, LLVM can no longer
store-to-load forward the forced feature bits into the ukernel's runtime
feature check across the enclosing loop, so the mmt4d/pack tile-func
select never devirtualizes and the microkernel is left out-of-line.

Split the two concerns: reserve only the alloca (the stack slot, the
actual cause of #24744) in the entry block, but keep the feature-bit
patch at the call site. The stores re-run per iteration but allocate no
stack, so the stack stays bounded while the forced bits remain adjacent
to the (inlined) load and fold as before, restoring devirtualization.

Assisted-by: Claude-Code

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Signed-off-by: Ege Beysel <beyselege@gmail.com>