RISCV: one last little nit to make it build and run

Change-Id: I6e9e1dff09c08079774f7d6e60e67a12760d37b4
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/7645
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
x86: Update the check for Forbidden global variables

Add a section .illegal_globals to romstage and check that the section does not
contain any variables while creating romstage.

[pg: Handle individual AGESA special cases in the
linker script instead of whitelisting everything
remotely AGESA related in the Makefile.]

Change-Id: I866681f51a44bc21770d32995c281b556a90c153
Signed-off-by: Furquan Shaikh <furquan@google.com>
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/7306
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>