scripts: make some scripts executable

Set the x bit to some scripts to make them directly executable.

Especially, scripts/checkdeclares.pl is not hooked by anyone.
It should be executable since it is tedious to type
'perl scripts/checkdeclares.pl'.

The original patch [1] set the x bit properly, but it was lost when
it was merged as commit 21917bde ("scripts: a new script for
checking duplicate struct declaration").

[1] https://lore.kernel.org/lkml/20210401110943.1010796-1-wanjiabing@vivo.com/Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>