Revert "riscv: image: Add new image type for RV64"

This reverts commit 14a4792a71db3561bea065415ac1f2ac69ef32b5 as
discussed in [1].

[1] https://lists.denx.de/pipermail/u-boot/2025-May/590841.html

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/include/image.h b/include/image.h
index 4620782..c1db838 100644
--- a/include/image.h
+++ b/include/image.h
@@ -138,8 +138,7 @@
 	IH_ARCH_ARC,			/* Synopsys DesignWare ARC */
 	IH_ARCH_X86_64,			/* AMD x86_64, Intel and Via */
 	IH_ARCH_XTENSA,			/* Xtensa	*/
-	IH_ARCH_RISCV,			/* RISC-V 32 bit*/
-	IH_ARCH_RISCV64,		/* RISC-V 64 bit*/
+	IH_ARCH_RISCV,			/* RISC-V */
 
 	IH_ARCH_COUNT,
 };