soc: soc_legacy: riscv: litex_vexriscv: Add updated paths

Adds updates paths for this SoC with the new riscv common folder
to prevent build failures until it is converted to hwmv2

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

soc/soc_legacy/riscv/litex_vexriscv/CMakeLists.txt

@@ -5,8 +5,8 @@
 #
 
 zephyr_sources(
-    ../common/riscv-privileged/soc_irq.S
-    ../common/riscv-privileged/vector.S
+    ${ZEPHYR_BASE}/soc/common/riscv/riscv-privileged/soc_irq.S
+    ${ZEPHYR_BASE}/soc/common/riscv/riscv-privileged/vector.S
 )
 
 set(SOC_LINKER_SCRIPT ${ZEPHYR_BASE}/include/zephyr/arch/riscv/common/linker.ld CACHE INTERNAL "")