IRQ routing path of Loongson-3:
Devices(most) --> I8259 --> HT Controller --> IRQ Routing Table --> CPU
^
|
Device(legacy devices such as UART) --> Bonito ---|

IRQ Routing Table route 32 INTs to CPU's INT0~INT3(IP2~IP5 of CP0), 32
INTs include 16 HT INTs(mostly), 4 PCI INTs, 1 LPC INT, etc. IP6 is used
for IPI and IP7 is used for internal MIPS timer. LOONGSON_INT_ROUTER_*
are IRQ Routing Table registers.

I8259 IRQs are 1:1 mapped to HT1 INTs. LOONGSON_HT1_* are configuration
registers of HT1 controller.

Signed-off-by: Huacai Chen
Signed-off-by: Hongliang Tao
Signed-off-by: Hua Yan
Tested-by: Alex Smith
Reviewed-by: Alex Smith
Cc: John Crispin
Cc: Steven J. Hill
Cc: Aurelien Jarno
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang
Cc: Zhangjin Wu
Patchwork: https://patchwork.linux-mips.org/patch/6634
Signed-off-by: Ralf Baechle