Remove generic system

The generic system has been broken for a long time and only adds
confusion. It has been more or less replaced with or1200-generic
elf-loader: add missing headers in vpi_wrapper.c

No error while using Icarus but Modelsim complains.

Add missing stdlib.h and ctype.h required for NULL, free() and
isspace().

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>