arm64: Fix NUMA build error when !CONFIG_ACPI

Since asm/acpi.h is only included by linux/acpi.h when CONFIG_ACPI is
enabled, disabling the latter leads to the following build error on
arm64:

arch/arm64/mm/numa.c: In function ‘arm64_numa_init’:
arch/arm64/mm/numa.c:395:24: error: ‘arm64_acpi_numa_init’ undeclared (first use in this function)
   if (!acpi_disabled && !numa_init(arm64_acpi_numa_init))

This patch include the asm/acpi.h explicitly in arch/arm64/mm/numa.c for
the arm64_acpi_numa_init() definition.

Fixes: d8b47fca ("arm64, ACPI, NUMA: NUMA support based on SRAT and SLIT")
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>