arch/Config.in.riscv: Remove BR2_RISCV_ISA_CUSTOM_RVA from BR2_riscv_custom

BR2_riscv_custom should only contain the basic I extension. The A
extension should be optional and selected by board configs.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

arch/Config.in.riscv

@@ -35,7 +35,6 @@ config BR2_riscv_g
 config BR2_riscv_custom
 	bool "Custom architecture"
 	select BR2_RISCV_ISA_RVI
-	select BR2_RISCV_ISA_CUSTOM_RVA
 
 endchoice