kernel/panic: allocate taint string buffer dynamically

kernel/panic: allocate taint string buffer dynamically

The buffer used to hold the taint string is statically allocated, which
requires updating whenever a new taint flag is added.

Instead, allocate the exact required length at boot once the allocator is
available in an init function.  The allocation sums the string lengths in
taint_flags[], along with space for separators and formatting.
print_tainted() is switched to use this dynamically allocated buffer.

If allocation fails, print_tainted() warns about the failure and continues
to use the original static buffer as a fallback.

Link: https://lkml.kernel.org/r/20260222140804.22225-1-rioo.tsukatsukii@gmail.com
Signed-off-by: Rio <rioo.tsukatsukii@gmail.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Wang Jinchao <wangjinchao600@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>