LoongArch: Increase COMMAND_LINE_SIZE up to 4096

The default COMMAND_LINE_SIZE of 512, inherited from asm-generic, is
too small for modern use cases. For example, kdump configurations or
extensive debugging parameters can easily exceed this limit.

Therefore, increase the command line size to 4096 bytes, aligning
LoongArch with the MIPS architecture. This change follows a broader
trend among architectures to raise this limit to support modern needs;
for instance, PowerPC increased its value for similar reasons in the
commit a5980d06 ("powerpc: Bump COMMAND_LINE_SIZE to 2048").

Similar to the change made for RISC-V in the commit 61fc1ee8
("riscv: Bump COMMAND_LINE_SIZE value to 1024"), this is considered
a safe change. The broader kernel community has reached a consensus
that modifying COMMAND_LINE_SIZE from UAPI headers does not constitute
a uABI breakage, as well-behaved userspace applications should not
rely on this macro.

Suggested-by: Huang Cun <cunhuang@tencent.com>
Signed-off-by: Ming Wang <wangming01@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>