plat/stm32: Implement fdt_read_uint32_default() as a wrapper

The STM32 platform code uses its own set of FDT helper functions,
although some of them are fairly generic.

Remove the implementation of fdt_read_uint32_default() and implement it
on top of the newly introduced fdt_read_uint32() function, then convert
all users over.

This also fixes two callers, which were slightly abusing the "default"
semantic.

Change-Id: I570533362b4846e58dd797a92347de3e0e5abb75
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/drivers/st/clk/stm32mp_clkfunc.c b/drivers/st/clk/stm32mp_clkfunc.c
index 6404d99..e87ab1b 100644
--- a/drivers/st/clk/stm32mp_clkfunc.c
+++ b/drivers/st/clk/stm32mp_clkfunc.c
@@ -151,7 +151,8 @@
 			continue;
 		}
 
-		return fdt_read_uint32_default(subnode, prop_name, dflt_value);
+		return fdt_read_uint32_default(fdt, subnode, prop_name,
+					       dflt_value);
 	}
 
 	return dflt_value;