brcm47xx: explicitly select CPU_MIPS32_R2 and CPU_MIPSR2 for mips74k

brcm47xx: explicitly select CPU_MIPS32_R2 and CPU_MIPSR2 for mips74k

The mips74k subtarget of brcm47xx configures gcc to compile for mips32r2;
however, the generated kernel config for 3.14 and later kernels ends up
with CPU_MIPS32_R1 and CPU_MIPSR1 selected.  The generated kernel config
for the 3.10 kernel (Barrier Breaker) properly selected CPU_MIPS32_R2 and
CPU_MIPSR2.  Modify the default kernel config for mips74k to explicitly
select CPU_MIPS32_R2 and CPU_MIPSR2.

Signed-off-by: Nathan Hintz <nlhintz@hotmail.com>
Tested-by: Rafał Miłecki <zajec5@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45469 3c298f89-4303-0410-b956-a3cf2f4a3e73