toolchain/glibc: Restrict ppc64le support to power8

Glibc restricts ppc64le support to Power8 (or later):

 https://sourceware.org/git/?p=glibc.git;a=commit;h=a27d2c19355a15569dfcdd5da741b57acf1a106a

The autobuilder has been attempting combiations of BR2_powerpc64le,
BR2_TOOLCHAIN_USES_GLIBC and

BR2_powerpc_970:

 http://autobuild.buildroot.net/results/89eae4c6e28658444ca5bc67caa2644358de97b7

BR2_powerpc_power6:

 http://autobuild.buildroot.net/results/bee990c9c34d391cfc4a351a30abc1a0a53a2415

BR2_powerpc_620:

 http://autobuild.buildroot.net/results/a0557172757d3bba2b5fc6244c7b9b17ef6be0db

When Power9, Power10, etc support is added to buildroot we may require a
BR2_PPC64LE_AT_LEAST_POWER8 or similar.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit e59b3acc3603e55fbaec25406258ec9ca9623564)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

toolchain/toolchain-buildroot/Config.in

@@ -46,7 +46,7 @@ config BR2_TOOLCHAIN_BUILDROOT_GLIBC
 	depends on BR2_arm         || BR2_armeb      || BR2_aarch64 || \
 		   BR2_aarch64_be  || BR2_i386       || BR2_mips    || \
 		   BR2_mipsel      || BR2_mips64     || BR2_mips64el|| \
-		   BR2_powerpc     || BR2_powerpc64  || BR2_powerpc64le || \
+		   BR2_powerpc     || BR2_powerpc64  || BR2_powerpc_power8 || \
 		   BR2_riscv       || BR2_s390x      || BR2_sh          || \
 		   BR2_sparc64     || BR2_x86_64     || BR2_microblaze  || \
 		   BR2_nios2       || (BR2_arc && BR2_ARC_ATOMIC_EXT)   || BR2_csky