soc: mmp: guard include of asm/cputype.h with CONFIG_ARM{,64}

Since this driver is enabled for COMPILE_TEST, it avoids build error
on x86 allmodconfig:

In file included from /build/drivers/phy/marvell/phy-mmp3-usb.c:12:
/build/include/linux/soc/mmp/cputype.h:5:10: fatal error: asm/cputype.h: No such file or directory

Link: https://lore.kernel.org/r/20191022015658.14624-1-olof@lixom.net


Signed-off-by: Olof Johansson <olof@lixom.net>