arm64: Constify struct kobj_type

'struct kobj_type' is not modified. It is only used in kobject_init()
which takes a 'const struct kobj_type *ktype' parameter.

Constifying this structure moves some data to a read-only section,
so increase over all security.

On a x86_64, compiled with arm defconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
   5602	    548	    352	   6502	   1966	arch/arm64/kernel/cpuinfo.o

After:
======
   text    data     bss     dec     hex filename
   5650     500     352    6502    1966 arch/arm64/kernel/cpuinfo.o

Signed-off-by: Huang Xiaojia <huangxiaojia2@huawei.com>
Link: https://lore.kernel.org/r/20240826151250.3500302-1-huangxiaojia2@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>