hexagon: mm: include asm/setup.h for setup_arch_memory()'s prototype

hexagon: mm: include asm/setup.h for setup_arch_memory()'s prototype

Clang warns:

  arch/hexagon/mm/init.c:138:13: warning: no previous prototype for function 'setup_arch_memory' [-Wmissing-prototypes]
    138 | void __init setup_arch_memory(void)
        |             ^
  arch/hexagon/mm/init.c:138:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
    138 | void __init setup_arch_memory(void)
        | ^
        | static

The prototype is in asm/setup.h, include it to clear up the warning.

Link: https://lkml.kernel.org/r/20231130-hexagon-missing-prototypes-v1-3-5c34714afe9e@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Brian Cain <bcain@quicinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>