curl: Reenable auth support for native and nativesdk

curl: Reenable auth support for native and nativesdk

148de08220c0ad390ec533e452cbaad7a9338204 adapted the recipe to
accomodate the newly introduced configure options for the various
authentication schemes supported by curl. However, support for these was
not added for the -native and -nativesdk variants of the recipe.

Fix this and introduce a PACKAGECONFIG variable for the flags common to
all recipe variants to avoid such regressions in the future.

Signed-off-by: Philip Lorenz <philip.lorenz@bmw.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>