d/control: Add build dependency on bc

The ls1028ardb platform is failing to build in CI with the following
error:

[  233s] plat/nxp/common/setup/ls_bl2_el3_setup.c: In function ‘ls_bl2_el3_plat_arch_setup’:
[  233s] <command-line>: error: invalid suffix "x" on integer constant
[  233s] plat/nxp/common/setup/ls_bl2_el3_setup.c:189:31: note: in expansion of macro ‘BL2_BASE’
[  233s]   189 |                               BL2_BASE,
[  233s]       |                               ^~~~~~~~

Looking at the definition of `BL2_BASE` we find:

BL2_BASE        :=      $(shell echo "0x"$$(echo "obase=16; ${BL2_BASE_ADDR}" | bc))

There is no dependency on `bc` in the packaging and thus this is
unlikely to be installed in the CI build environment. Add this
dependency.

Note: This change is only needed as long as we are supporting the
      ls1028ardb and associated platforms.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

debian/control

@@ -9,7 +9,8 @@ Build-Depends: debhelper-compat (= 13),
  libssl-dev <!pkg.arm-trusted-firmware.notools>,
  openssl,
  u-boot-layerscape [arm64],
- qoriq-rcw [arm64]
+ qoriq-rcw [arm64],
+ bc [arm64]
 Rules-Requires-Root: no
 Homepage: https://www.trustedfirmware.org/
 Vcs-Browser: https://salsa.debian.org/debian/arm-trusted-firmware