scripts/gdb: add $lx_clk_core_lookup function

Finding an individual clk_core requires walking the tree which can be
quite complicated so add a helper for easy access.

(gdb) print *(struct clk_scu*)$lx_clk_core_lookup("uart0_clk")->hw

Link: http://lkml.kernel.org/r/Message-ID:
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>