treewide: fix syntax errors exposed after kconfig update

treewide: fix syntax errors exposed after kconfig update

After commit e82a4d9cfb ("config: regenerate *_shipped sources") the mconf
parser became more strict as a side effect and started to spew a series of
warnings when evaluating our generated kconfig sources:

  tmp/.config-package.in:705:warning: ignoring unsupported character '@'

The root cause of these warnings is a wrong use of the @SYMBOL dependency
syntax in various Makefile. Fix the corresponding Makefiles by turning
`@SYM||@SYM2` expressions into the proper `@(SYM||SYM2)` form.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>