hw/intc/loongson_ipi: Expose loongson_ipi_core_read/write helpers

hw/intc/loongson_ipi: Expose loongson_ipi_core_read/write helpers

In order to access loongson_ipi_core_read/write helpers
from loongson_ipi_common.c in the next commit, make their
prototype declaration public.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
[PMD: Extracted from bigger commit, added commit description]
Co-Developed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Bibo Mao <maobibo@loongson.cn>
Acked-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Tested-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <20240805180622.21001-11-philmd@linaro.org>