docs/scripts/gdb: add necessary make scripts_gdb step

stable inclusion
from stable-v5.10.173
commit fcfc7740228d2a4ce105950a41494ede86712d09
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8BFR3

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fcfc7740228d2a4ce105950a41494ede86712d09



--------------------------------

[ Upstream commit 6b219431 ]

In order to debug the kernel successfully with gdb you need to run
'make scripts_gdb' nowadays.

This was changed with the following commit:

Commit 67274c08 ("scripts/gdb: delay generation of gdb
constants.py")

In order to have a complete guide for beginners this remark
should be added to the offial documentation.

Signed-off-by: Jakob Koschel <jkl820.git@gmail.com>
Link: https://lore.kernel.org/r/20230112-documentation-gdb-v2-1-292785c43dc9@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>