Revert "Disable dexpreopt for aosp_riscv64"

This reverts commit ae7f543b7c95715f9df80671d4a89b90d48c108e.

Reason for revert: Enabling dexpreopt for RISC-V (there is still no
  compiler support, but dex2oat runs in verification mode and does
  not attempt any compilation with https://r.android.com/2510739).

Change-Id: I0a6d0416bec51131f0a54c7ff5b0e194728452b1
diff --git a/core/board_config.mk b/core/board_config.mk
index 16acdde..b1b7b81 100644
--- a/core/board_config.mk
+++ b/core/board_config.mk
@@ -204,10 +204,7 @@
 
 # Conditional to building on linux, as dex2oat currently does not work on darwin.
 ifeq ($(HOST_OS),linux)
-  # TODO(riscv64) add compiler support and enable dexpreopt on RISC-V.
-  ifneq ($(TARGET_ARCH),riscv64)
-    WITH_DEXPREOPT := true
-  endif
+  WITH_DEXPREOPT := true
 endif
 
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