omap3_beagle: Update for DM SPL support

- Switch to using the omap3-u-boot.dtsi file for needed properties.
- Remove a few SPL features to free up more SRAM space.
- Switch CONFIG_SYS_TEXT_BASE to the normal default, we don't need to
  worry about X-Loader at this point anymore.
- A few related updates to SPL options as part of switching to DM SPL.

Signed-off-by: Tom Rini <trini@konsulko.com>
Tested-by: Derald D. Woods <woods.technical@gmail.com>

arch/arm/dts/omap3-beagle-u-boot.dtsi

@@ -5,20 +5,10 @@
  * (C) Copyright 2017 Derald D. Woods <woods.technical@gmail.com>
  */
 
+#include "omap3-u-boot.dtsi"
+
 / {
 	chosen {
 		stdout-path = &uart3;
 	};
 };
-
-&uart1 {
-	reg-shift = <2>;
-};
-
-&uart2 {
-	reg-shift = <2>;
-};
-
-&uart3 {
-	reg-shift = <2>;
-};

arch/arm/dts/omap3-beagle-xm-ab-u-boot.dtsi

@@ -5,20 +5,10 @@
  * (C) Copyright 2017 Derald D. Woods <woods.technical@gmail.com>
  */
 
+#include "omap3-u-boot.dtsi"
+
 / {
 	chosen {
 		stdout-path = &uart3;
 	};
 };
-
-&uart1 {
-	reg-shift = <2>;
-};
-
-&uart2 {
-	reg-shift = <2>;
-};
-
-&uart3 {
-	reg-shift = <2>;
-};

arch/arm/dts/omap3-beagle-xm-u-boot.dtsi

@@ -5,20 +5,10 @@
  * (C) Copyright 2017 Derald D. Woods <woods.technical@gmail.com>
  */
 
+#include "omap3-u-boot.dtsi"
+
 / {
 	chosen {
 		stdout-path = &uart3;
 	};
 };
-
-&uart1 {
-	reg-shift = <2>;
-};
-
-&uart2 {
-	reg-shift = <2>;
-};
-
-&uart3 {
-	reg-shift = <2>;
-};