arm, arm926ejs: Add option CONFIG_SYS_EXCEPTION_VECTORS_HIGH

arm, arm926ejs: Add option CONFIG_SYS_EXCEPTION_VECTORS_HIGH

The V bit of the c1 register of CP15 should not be cleared on DA850
SoCs since they have no valid memory at 0x00000000. This patch
introduces a configuration option CONFIG_SYS_EXCEPTION_VECTORS_HIGH
that allows setting the correct value for the V bit.

Signed-off-by: Christian Riesch <[email protected]>
Reported-by: Sughosh Ganu <[email protected]>
Cc: Albert Aribaud <[email protected]>
Cc: Tom Rini <[email protected]>
Cc: Sughosh Ganu <[email protected]>
Cc: Heiko Schocher <[email protected]>