eficonfig: increase the number of menu entries

Current eficonfig has the maximum number of menu entries and
it is 99. If there are more EFI load options and files in the
system, eficonfig can not handle it.

This commit increases this maximum number of menu entries
to INT_MAX.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>