x86/bpf: Make arch_bpf_trampoline_size allocate from EXECMEM_MODULE_DATA

Jiri Olsa reports slowdown of tracing_multi benchmark that allocates huge
number of trampolines [1].

The slowdown caused by extra protection changes in execmem_alloc_rw() and
execmem_free().

With ROX caches enabled, all execmem allocations except EXECMEM_MODULE_DATA
are ROX after the allocation. execmem_alloc_rw() temporarily sets them to
W+NX and execmem_free() resets them back to ROX.

The only user of bpf_jit_alloc_exec_rw() is x86::arch_bpf_trampoline_size()
that only needs a temporary writable buffer in the modules address space.

On x86 executable memory and module data are constrained to the same
address range, so x86::arch_bpf_trampoline_size() can directly use
execmem_alloc(EXECMEM_MODULE_DATA)

Replace the call to bpf_jit_alloc_exec_rw() with a call to
execmem_alloc(EXECMEM_MODULE_DATA) in x86::arch_bpf_trampoline_size() and
drop bpf_jit_alloc_exec_rw() helper.

Fixes: 5bf02dbf39fa ("bpf, x86: Make sure allocation in arch_bpf_trampoline_size() is writable")
Reported-by: Jiri Olsa <olsajiri@gmail.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/all/an8r7EODLIL-bZM3@krava
Link: https://lore.kernel.org/bpf/20260818130510.3110054-1-rppt@kernel.org

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