gdb: Add extra early initialization symbols for i386-pc

gdb: Add extra early initialization symbols for i386-pc

Add symbols for boot.image, disk.image, and lzma_decompress.image if the
target is i386-pc. This is only done for i386-pc because that is the only
target that uses the images. By loading the symbols for these images,
these images can be more easily debugged by allowing the setting of break-
points in that code and to see easily get the value of data symbols.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>