ARM: prima2: do not select SMP_ON_UP

The new Atlas7 platform implicitly selects 'CONFIG_SMP_ON_UP',
which leads to problems if we enable building the platform without
MMU, as that combination is not allowed and causes a link error:

arch/arm/kernel/built-in.o: In function `c_show':
:(.text+0x1872): undefined reference to `smp_on_up'
:(.text+0x1876): undefined reference to `smp_on_up'
arch/arm/kernel/built-in.o: In function `arch_irq_work_raise':
:(.text+0x3d48): undefined reference to `smp_on_up'
:(.text+0x3d4c): undefined reference to `smp_on_up'
arch/arm/kernel/built-in.o: In function `smp_setup_processor_id':
:(.init.text+0x180): undefined reference to `smp_on_up'

This removes the 'select' statement.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 4cba0585

 ("ARM: sirf: add Atlas7 machine support")
Acked-by: Barry Song <Baohua.Song@csr.com>
Cc: Zhiwu Song <Zhiwu.Song@csr.com>