templates: Don't use c_symbol for private symbols

Many uses of c_symbol are no longer needed due to historical
refactorings. Removing them should improve readability and rendering
performance.

Remove --fsupport-init flag support

This flag was mostly redundant as it is used by default and there are
no longer any motivating uses for not providing init support.

Move component init interfaces to libsel4camkes

These functions are constant and will always be defined by all components and so there is need
for them to be templated. Removing them specifically from the component header also removes the
implication that they should be called by component code when they are intended for internal use
by CAmkES only.

Finally putting these definitions in a library allows them to be used by other library code in
the future, as libraries cannot include per component templates.

Refactor component.template.c into multiple files

Prepares the way for supporting different environments by moving the C specific environment
code into a separate file.