gnome-system-monitor: Add dependency on gnome-icon-theme

Without this, the configure stage of this recipe fails with pkg-config not finding
the gnome-icon-theme package

Signed-off-by: Joel A Fernandes <agnel.joel@gmail.com>
Cc: jdk@ti.com
Cc: k-kooi@ti.com
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>