doc: rename Freescale to NXP

Freescale Semiconductor, Inc. was merged into NXP Semiconductors in 2015.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/board/index.rst b/doc/board/index.rst
index 9e90978..3308707 100644
--- a/doc/board/index.rst
+++ b/doc/board/index.rst
@@ -14,11 +14,11 @@
    congatec/index
    coreboot/index
    emulation/index
-   freescale/index
    google/index
    intel/index
    kontron/index
    microchip/index
+   nxp/index
    openpiton/index
    qualcomm/index
    rockchip/index