fix(gicv3/multichip): fix overflow caused by left shift

When spi_id_max is 5119, the expression `(spi_id_max - 4096U + 1U >> 5)`
evaluates to 32 leading to undefined behavior when using it to left
shift 1. Fix this undefined behavior.

Reported-by coverity scan:
https://lists.trustedfirmware.org/archives/list/tf-a@lists.trustedfirmware.org/thread/RMB4U7COL6IONZWEGF2FWXOQ6FPDIT4U/



```
    large_shift: In expression 1 << (spi_id_max - 4096U + 1U >> 5), left
    shifting by more than 31 bits has undefined behavior. The shift
    amount, spi_id_max - 4096U + 1U >> 5, is as much as 32.
```

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I5e77a78b81a6d0367875e7ea432a82b6ba0e587c