ARM: 6933/1: SPEAR6xx: Rename spear600_defconfig as spear6xx_defconfig

Reviewed-by: Stanley Miao <stanley.miao@windriver.com>
Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Rajeev Kumar <rajeev-dlh.kumar@st.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>