build: Replace variant patterns with a list

Replace the variant patterns in the default-by-variant list with an
explicit list of matching BSPs.

The change was tested by comparing the output of

  ./waf bspdefaults

before and after the change.

spec/build/bsps/dev/irq/optarmgic-icc-bpr0.yml

@@ -9,7 +9,19 @@ default: 0x00000002
 default-by-variant:
 - value: null
   variants:
-  - aarch64/.*
+  - aarch64/a53_ilp32_qemu
+  - aarch64/a53_lp64_qemu
+  - aarch64/a72_ilp32_qemu
+  - aarch64/a72_lp64_qemu
+  - aarch64/raspberrypi4b
+  - aarch64/xilinx_versal_aiedge
+  - aarch64/xilinx_versal_qemu
+  - aarch64/xilinx_versal_vck190
+  - aarch64/xilinx_zynqmp_ilp32_qemu
+  - aarch64/xilinx_zynqmp_ilp32_zu3eg
+  - aarch64/xilinx_zynqmp_lp64_cfc400x
+  - aarch64/xilinx_zynqmp_lp64_qemu
+  - aarch64/xilinx_zynqmp_lp64_zu3eg
 description: |
   Defines the initial value of the ICC_BPR0 register of the ARM GIC CPU
   Interface.  The value is optional.  If it is not defined, then the register

spec/build/bsps/dev/irq/optarmgic-icc-igrpen0.yml

@@ -9,7 +9,19 @@ default: 0x00000001
 default-by-variant:
 - value: null
   variants:
-  - aarch64/.*
+  - aarch64/a53_ilp32_qemu
+  - aarch64/a53_lp64_qemu
+  - aarch64/a72_ilp32_qemu
+  - aarch64/a72_lp64_qemu
+  - aarch64/raspberrypi4b
+  - aarch64/xilinx_versal_aiedge
+  - aarch64/xilinx_versal_qemu
+  - aarch64/xilinx_versal_vck190
+  - aarch64/xilinx_zynqmp_ilp32_qemu
+  - aarch64/xilinx_zynqmp_ilp32_zu3eg
+  - aarch64/xilinx_zynqmp_lp64_cfc400x
+  - aarch64/xilinx_zynqmp_lp64_qemu
+  - aarch64/xilinx_zynqmp_lp64_zu3eg
 description: |
   Defines the initial value of the ICC_IGRPEN0 register of the ARM GIC CPU
   Interface.  The value is optional.  If it is not defined, then the register