soc: arm: bcm_vk: viper: Increase default NUM_IRQS

Maximum GIC SPI is 228, so maximum INTID is 228 + 32 = 260.
So, _sw_isr_table needs to support 260 entries

Signed-off-by: Raveendra Padasalagi <raveendra.padasalagi@broadcom.com>
Signed-off-by: Abhishek Shah <abhishek.shah@broadcom.com>