ARM: pxa/mmp: remove traces of plat-pxa

The missing include directory caused a W=1 warning that can be
trivially fixed. I also noticed references in the marvell.rst
documentation that can be removed at the same time.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Documentation/arm/marvell.rst

@@ -374,8 +374,6 @@ PXA 2xx/3xx/93x/95x family
 
    Linux kernel mach directory:
 	arch/arm/mach-pxa
-   Linux kernel plat directory:
-	arch/arm/plat-pxa
 
 MMP/MMP2/MMP3 family (communication processor)
 ----------------------------------------------
@@ -429,8 +427,6 @@ MMP/MMP2/MMP3 family (communication processor)
 
    Linux kernel mach directory:
 	arch/arm/mach-mmp
-   Linux kernel plat directory:
-	arch/arm/plat-pxa
 
 Berlin family (Multimedia Solutions)
 -------------------------------------
@@ -518,9 +514,6 @@ Long-term plans
    Business Unit) in a single mach-<foo> directory. The plat-orion/
    would therefore disappear.
 
- * Unify the mach-mmp/ and mach-pxa/ into the same mach-pxa
-   directory. The plat-pxa/ would therefore disappear.
-
 Credits
 -------
 

arch/arm/mach-mmp/Makefile

@@ -2,8 +2,6 @@
 #
 # Makefile for Marvell's PXA168 processors line
 #
-ccflags-$(CONFIG_ARCH_MULTIPLATFORM) := -I$(srctree)/arch/arm/plat-pxa/include
-
 obj-y				+= common.o devices.o time.o
 
 # SoC support