MIPS: Loongson64: Drop 32-bit support for Loongson 2E/2F devices

The 32-bit support was broken at runtime, it doesn't boot anymore,
witch is hard to debug because even early printk isn't working, also
there are some build warnings. Some newer bootloader may not support
32-bit ELF. So we decide to drop 32-bit support.

Make loongson64 a pure 64-bit arch.

Signed-off-by: Jiaxun Yang <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Huacai Chen <[e-mail]>
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/18174/
Signed-off-by: James Hogan <[e-mail]>

arch/mips/loongson64/Kconfig

···
 	select I8259
 	select ISA
 	select IRQ_MIPS_CPU
-	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_64BIT_KERNEL
 	select SYS_SUPPORTS_LITTLE_ENDIAN
 	select SYS_SUPPORTS_HIGHMEM
···
 	select ISA
 	select SYS_HAS_CPU_LOONGSON2F
 	select SYS_HAS_EARLY_PRINTK
-	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_64BIT_KERNEL
 	select SYS_SUPPORTS_HIGHMEM
 	select SYS_SUPPORTS_LITTLE_ENDIAN