scripts: use CT_CONFIG_SHELL instead of CT_SHELL

CT_SHELL is undefined.
Thus, the generated wrapper scripts are not executable by the kernel
because they do not contain a valid interpreter.
Use CT_CONFIG_SHELL instead.

Signed-off-by: "Titus von Boxberg" <titus@v9g.de>
(transplanted from cf509170838f4e289fe25617e3f3db1d6d6ffc41)

# Alpha specific configuration file

## select ARCH_SUPPORTS_32

## select ARCH_DEFAULT_32

## select ARCH_USE_MMU

## select ARCH_SUPPORT_CPU

## select ARCH_SUPPORT_TUNE

##

## help The Alpha architecture.