drivers: clk: add fu740 support

Add fu740 support. One abstract layer is added for supporting
multiple chips such as fu540 and fu740.

Signed-off-by: Green Wan <green.wan@sifive.com>
diff --git a/drivers/clk/sifive/Kconfig b/drivers/clk/sifive/Kconfig
index c4d0a1f..20fc004 100644
--- a/drivers/clk/sifive/Kconfig
+++ b/drivers/clk/sifive/Kconfig
@@ -6,11 +6,11 @@
 	help
 	  SoC drivers for SiFive Linux-capable SoCs.
 
-config CLK_SIFIVE_FU540_PRCI
-	bool "PRCI driver for SiFive FU540 SoCs"
+config CLK_SIFIVE_PRCI
+	bool "PRCI driver for SiFive SoCs"
 	depends on CLK_SIFIVE
 	select CLK_ANALOGBITS_WRPLL_CLN28HPC
 	help
 	  Supports the Power Reset Clock interface (PRCI) IP block found in
-	  FU540 SoCs.  If this kernel is meant to run on a SiFive FU540 SoC,
-	  enable this driver.
+	  FU540/FU740 SoCs. If this kernel is meant to run on a SiFive FU540/
+	  FU740 SoCs, enable this driver.