scripts/gdb: fix invocation when CONFIG_COMMON_CLK is not set

CLK_GET_RATE_NOCACHE depends on CONFIG_COMMON_CLK. Importing constants.py
when CONFIG_COMMON_CLK is not defined causes:

(gdb) lx-symbols
(...)
File "scripts/gdb/linux/proc.py", line 15, in <module>
from linux import constants
File "scripts/gdb/linux/constants.py", line 2, in <module>
LX_CLK_GET_RATE_NOCACHE = gdb.parse_and_eval("CLK_GET_RATE_NOCACHE")
gdb.error: No symbol "CLK_GET_RATE_NOCACHE" in current context.

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: e7e6f462c1be ("scripts/gdb: print cached rate in lx-clk-summary")
Signed-off-by: Fabiano Rosas <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Cc: Jan Kiszka <[e-mail]>
Cc: Kieran Bingham <[e-mail]>
Cc: Leonard Crestez <[e-mail]>
Cc: Jackie Liu <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

scripts/gdb/linux/constants.py.in

···
 import gdb
 
 /* linux/clk-provider.h */
-LX_GDBPARSED(CLK_GET_RATE_NOCACHE)
+if IS_BUILTIN(CONFIG_COMMON_CLK):
+    LX_GDBPARSED(CLK_GET_RATE_NOCACHE)
 
 /* linux/fs.h */
 LX_VALUE(SB_RDONLY)