powerpc: Remove ARCH= references from documentation

When building U-Boot we select the architecture via Kconfig and not ARCH
being passed in via the environment or make cmdline.

Cc: Po Liu <po.liu@nxp.com>
Cc: Qiang Zhao <qiang.zhao@nxp.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/freescale/c29xpcie/README b/board/freescale/c29xpcie/README
index 2e249cb..a6120f1 100644
--- a/board/freescale/c29xpcie/README
+++ b/board/freescale/c29xpcie/README
@@ -56,7 +56,6 @@
 Build and program U-Boot to NOR flash
 ==================================
 1. Build u-boot.bin image example:
-	export ARCH=powerpc
 	export CROSS_COMPILE=/your_path/powerpc-linux-gnu-
 	make C293PCIE
 
diff --git a/board/freescale/p1010rdb/README.P1010RDB-PA b/board/freescale/p1010rdb/README.P1010RDB-PA
index 105942f..46c6123 100644
--- a/board/freescale/p1010rdb/README.P1010RDB-PA
+++ b/board/freescale/p1010rdb/README.P1010RDB-PA
@@ -98,7 +98,6 @@
 Build and burn U-Boot to NOR flash
 ==================================
 1. Build u-boot.bin image
-	export ARCH=powerpc
 	export CROSS_COMPILE=/your_path/powerpc-linux-gnu-
 	make P1010RDB_NOR
 
diff --git a/board/freescale/p1010rdb/README.P1010RDB-PB b/board/freescale/p1010rdb/README.P1010RDB-PB
index dc82f0d..4a3b389 100644
--- a/board/freescale/p1010rdb/README.P1010RDB-PB
+++ b/board/freescale/p1010rdb/README.P1010RDB-PB
@@ -128,7 +128,6 @@
 Build images for different boot mode
 ====================================
 First setup cross compile environment on build host
-   $ export ARCH=powerpc
    $ export CROSS_COMPILE=<your-compiler-path>/powerpc-linux-gnu-
 
 1. For NOR boot