scripts/gdb: add GDB convenience functions $lx_dentry_name() and $lx_i_dentry()

scripts/gdb: add GDB convenience functions $lx_dentry_name() and $lx_i_dentry()

$lx_dentry_name() generates a full VFS path from a given dentry pointer,
and $lx_i_dentry() returns the dentry pointer associated with the given
inode pointer, if there is one.

Link: https://lkml.kernel.org/r/c9a5ad8efbfbd2cc6559e082734eed7628f43a16.1677631565.git.development@efficientek.com
Signed-off-by: Glenn Washburn <development@efficientek.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Antonio Borneo <antonio.borneo@foss.st.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>