[PATCH][GAS][AArch64] Update Cortex-X1 feature flags

This is feature flags update for Cortex-X1 CPU.
For more information about this processor, see [0].

[0] : https://www.arm.com/products/cortex-x

gas/ChangeLog:

2020-10-05  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>

	* config/tc-aarch64.c: Update Cortex-X1 feature flags.