perf beauty mmap_flags: Check if the arch has a mmap.h file

perf beauty mmap_flags: Check if the arch has a mmap.h file

If not, then just use what is in asm-generic. This fixes the build for
my sh4, m68k and riscv64 perf test build containers that were failing
due to b2b508653d12 ("perf beauty: Add a generator for MAP_ mmap's flag
constants"), that were not covered in the cset introducing those
tools/arch/*/include/uapi/asm/mman.h files.

  230aab24ea90 ("tools include: Add uapi mman.h for each architecture")

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: b2b508653d12 ("perf beauty: Add a generator for MAP_ mmap's flag constants")
Link: https://lkml.kernel.org/n/tip-rpy9t2e0wxpnum1yvxhreafe@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>