riscv: sifive: fu540: Enable SiFive PWM driver

This patch enables SiFive PWM driver for the SiFive
Unleashed board.

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
diff --git a/board/sifive/fu540/Kconfig b/board/sifive/fu540/Kconfig
index 86193d7..683668d 100644
--- a/board/sifive/fu540/Kconfig
+++ b/board/sifive/fu540/Kconfig
@@ -65,5 +65,7 @@
 	imply SMP
 	imply MISC
 	imply SIFIVE_OTP
+	imply DM_PWM
+	imply PWM_SIFIVE
 
 endif