tools: Fix bitfield dependency failure

A perf build failure was reported by Thomas Voegtle on stable kernel
v6.6.120:

    CC      tests/sample-parsing.o
    CC      util/intel-pt-decoder/intel-pt-pkt-decoder.o
    CC      util/perf-regs-arch/perf_regs_csky.o
    CC      util/arm-spe-decoder/arm-spe-pkt-decoder.o
    CC      util/perf-regs-arch/perf_regs_loongarch.o
  In file included from util/arm-spe-decoder/arm-spe-pkt-decoder.h:10,
                   from util/arm-spe-decoder/arm-spe-pkt-decoder.c:14:
  /local/git/linux-stable-rc/tools/include/linux/bitfield.h: In function ‘le16_encode_bits’:
  /local/git/linux-stable-rc/tools/include/linux/bitfield.h:166:31: error: implicit declaration of
  function ‘cpu_to_le16’; did you mean ‘htole16’? [-Werror=implicit-function-declaration]
    ____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \
                                 ^~~~~~~~~
  /local/git/linux-stable-rc/tools/include/linux/bitfield.h:149:9: note: in definition of macro
  ‘____MAKE_OP’
    return to((v & field_mask(field)) * field_multiplier(field)); \
           ^~
  /local/git/linux-stable-rc/tools/include/linux/bitfield.h:170:1: note: in expansion of macro
  ‘__MAKE_OP’
   __MAKE_OP(16)

Fix this by including linux/kernel.h, which provides the required
definitions.

The issue was not found on the mainline due to the relevant C files have
included kernel.h.  It'd be good to merge this change on mainline
as well for robustness.

Fixes: 64d86c0 ("perf arm-spe: Extend branch operations")
Reported-by: Thomas Voegtle <tv@lio96.de>
Closes: https://lore.kernel.org/stable/3a44500b-d7c8-179f-61f6-e51cb50d3512@lio96.de/
To: Greg KH <gregkh@linuxfoundation.org>
To: Sasha Levin <sashal@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Leo Yan <leo.yan@arm.com>

Author: Leo-Yan

tools/include/linux/bitfield.h

@@ -8,6 +8,7 @@
 #define _LINUX_BITFIELD_H
 
 #include <linux/build_bug.h>
+#include <linux/kernel.h>
 #include <asm/byteorder.h>
 
 /*